<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <meta name="Generator" content="Microsoft Word 97"> <meta name="GENERATOR" content="Microsoft FrontPage 4.0"> <title>OOP/C++/Programming Glossary</title> </head> <body link="#0000FF" vlink="#800080"> <font face="Arial"><a href="../../copyright.htm" target="_blank">Copyright 1995-2002</a>&nbsp;<a href="http://www.mza.com" target="_top"> MZA Associates Corporation</a></font> <p align="left"><b><font face="Arial" size="6">tempus Glossary</font></b></p> <p><font face="Arial"><b><a href="#connect_operator_right">Symbols</a> <a href="#advanceTime">A</a> <a href="#Base class">B</a> <a href="#C++">C</a> <a href="#Data member">D</a> <a href="#event"> E</a> <a href="#float">F</a> <a href="#Grid"> G</a> <a href="#h_file">H</a> <a href="#include_file">I</a> J K <a href="#Lazy evaluation"> L</a> <a href="#Member function"> M</a> <a href="#now"> N</a> <a href="#object"> O</a> <a href="#Parameter"> P</a> Q <a href="#Recallable"> R</a> <a href="#SaveVariable"> S</a> <a href="#template"> T</a> <a href="#Universe"> U</a> <a href="#value"> V</a> <a href="#work_directory"> W</a> X Y Z</b></font></p> <hr> <p><font face="Arial" size="3">This glossary is intended to help current and prospective tempus users gain a better understanding of how tempus works, and how it can be used. We have tried to provide definitions for all unfamiliar or specially defined terms likely to be encountered in the course of using the tempus visual editor and/or working with tempus at the source code level; if you find any omissions, please email us at <b><a href="mailto:tempus@mza.com">tempus@mza.com</a></b>. For the convenience of those less familiar with object-oriented programming (OOP) and C++, we have included some of that terminology as well; for a more thorough treatment see <u>The C++ Programming Language</u> by Bjarne Stroustrup. Among the terms defined are a number of C++ classes, functions, and operators; all C++ source code appears in a fixed font to distinguish it from ordinary text. Class names and operators are indicated by parenthetical comments, while function names are indicated by empty parentheses. Only the most commonly encountered classes and functions are documented here; for complete source code documentation see the <i>tempus Programmer s Manual</i>. All terms appearing in italics in definitions are themselves defined in the glossary.</font> <p><font face="Arial" size="3"><a NAME="connect_operator_right"></a><b><a name="=&gt;&gt; (C++ operator)">=>> (C++ operator)</a></b> <br>a C++ binary operator used to establish connections between subsystem outputs or external inputs (on the left side) and subsystem inputs or external outputs (on the right side).</font> <p><font face="Arial" size="3"><a NAME="connect_operator_left"></a><b><a name="&lt;&lt;= (C++ operator)">&lt;&lt;= (C++ operator)</a></b> <br>a C++ binary operator used to establish connections between subsystem outputs or external inputs (on the right side) and subsystem inputs or external outputs (on the left side).</font> <p><font face="Arial" size="3"><a NAME="advanceTime"></a><b><a name="advanceTime()">advanceTime()</a></b> <br>A global function used to control the advance of virtual time in the current default virtual universe. advanceTime() takes a single argument specifying the amount by which the virtual time is to be advanced.</font> <p><font face="Arial" size="3"><a NAME="advanceTimeUntil"></a><b><a name="advanceTimeUntil()">advanceTimeUntil()</a></b> <br>A global function used to control the advance of virtual time in the current default virtual universe. advanceTimeUntil() takes a single argument specifying the time to which the virtual time is to be advanced.</font> <p><font face="Arial" size="3"><a NAME="atomic_system_class"></a><b><a name="Atomic system class">Atomic system class</a></b> <br>A system class which contains no subsystems. Generally the .h file for an atomic system class will have been modified by hand in order to define the behavior desired by the system class designer; otherwise systems of the class would simply be inert. Defining the behavior would involve overriding one or more of the four <i>respondTo- methods</i>, possibly adding logic to the constructor and/or destructor, and possibly adding additional data members and/or member functions. For system classes with simple behaviors the designer may choose to keep complete implementation may be in kept .h file, but for more complex behaviors it is good practice to put the logic in a separate .cpp file, to permit separate compilation. See also <i>system class</i>, <i>.h file</i>, <i>.cpp file</i>, <i>respondTo- methods.</i> </font> <p><font face="Arial" size="3"><a NAME="base_class"></a><b><a name="Base class">Base class</a></b> <br>A class from which another more specialized class is derived, which defines a portion of the interface and/or implementation of the derived class. See also <i>derived class</i>.</font> <p><font face="Arial" size="3"><a NAME="binary_operator"></a><b>Binary operator</b> <br>An operator such as + or = which takes two arguments, which appear on either side of the operator. Apart from the syntax, a binary operator is exactly equivalent to a function taking two arguments. A binary operator can be defined either as a global function, or as a member function of its first (left side) argument.</font> <p style="word-spacing: 1; margin: 0">&nbsp; <p style="word-spacing: 1; margin: 0"><font face="Arial" size="3"><a NAME="bool"></a><b>bool</b></font> <p style="word-spacing: 1; margin: 0"><font size="3" face="Arial">(C++ intrinsic type)</font> <p class=MsoNormal style="word-spacing: 1; margin: 0"><font size="3" face="Arial">bool is a C++ intrinsic type used to represent Boolean (true/false) values.</font></p> <p><font face="Arial" size="3"><a NAME="cpp"></a><b><a name="C++">C++</a></b> <br>One of the most widely used object-oriented programming languages (OOPL).</font> <p class=MsoNormal style="word-spacing: 0; margin: 0">&nbsp;</p> <p class=MsoNormal style="word-spacing: 0; text-indent: 0; margin: 0"><a name="The C++ Programming Language"><font face="Arial"><b>The C++ Programming Language</b></font></a></p> <h1 style="word-spacing: 0; text-indent: 0; margin: 0"><font face="Arial" size="2">The C++ Programming Language, Bjarne Stroustrup, Addison-Wesley, ISBN 0-201-88954-4 and 0-201-70073-5. <span style="mso-spacerun: yes"></span>http://www.research.att.com/~bs/3rd.html</font></h1> <p><font face="Arial" size="3"><a NAME="cpp_code"></a><b>&quot;<a name="C++ code&quot;">C++ code"</a></b> <br>There are two places in the visual editor where the user can type in C++ source code to be inserted into the automatically generated source code. One is in the <i>system class edit window</i>, for code to be inserted in the system class .h file before the class declaration, and is typically used to put in include statements for C++ header files which define functions and/or constants for use in setting expressions. Other possible applications would include defining functions or constants in-line, or precomputing results needed in multiple setting expressions. The second place is in the <i>run set edit window</i>, for code to be inserted at the top of the main program, and is used in much the same way.</font> <p><font face="Arial" size="3"><a NAME="cancelEvent"></a><b><a name="cancelEvent()">cancelEvent()</a></b> <br>A method of class System used in system classes to cancel previously scheduled events. cancelEvent() takes one argument, of type EventId, used to specify which event is to be canceled. (The EventId for an event is the return value of scheduleEvent.)</font> <p><font face="Arial" size="3"><a NAME="cancelEvents"></a><b><a name="cancelEvents()">cancelEvents()</a></b> <br>a method of class System used in system classes to cancel all previously scheduled events. cancelEvents() takes no arguments.</font> <p><font face="Arial" size="3"><a NAME="class"></a><b>Class</b> <br>One of the key concepts in object-oriented programming, a class is the most general kind of user-defined type, defining both the state information used by objects of the class (data members) and their behavior (member functions). Classes may be related to one another via <i>inheritance</i> relationships, wherein <i>base classes</i> define portions of the interface and/or implementation of <i>derived classes</i>.</font><p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="Complex"></a><b><a name="Complex &nbsp;(C++ class)">Complex <span style="mso-spacerun: yes"></span>(C++ class)</a></b></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">Complex is a C++ class, part of the tempus support libraries, use to represent complex numbers.<span style="mso-spacerun: yes"> </span>The memory layout exactly matches the way complex numbers are stored in Fortran, so that complex numbers and arrays can be passed between Fortran and C++.<span style="mso-spacerun: yes"> </span>In the near future all occurrences of Complex in tempus will be replaced with complex&lt;float&gt;, which shares the same memory layout, and is part of the new ANSI standard for C++.</font></p> <p><font face="Arial" size="3"><a NAME="composite_system_class"></a><b><a name="Composite system class">Composite system class</a></b> <br>A system class with contains one or more subsystems. Unlike an atomic system class, the .h file for a composite system class would normally be hand-modified. Instead, the behavior of a composite system is defined by the behaviors of its subsystems, their parameter settings, and the way they are connected. See also <i>system class</i>, <i>atomic system class</i>.</font><p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="Connection"></a><b>Connection</b></font><p style="word-spacing: 0; margin: 0"><font face="Arial" size="3">A  connection in tempus refers to a relationship established between an object used to refer some other object, e.g. a subsystem input, and another object which serves as the referent for the first object, e.g. a subsystem output.<span style="mso-spacerun: yes"> </span>Connections are represented graphically in the GUI as arrows from the referent objects to the reference objects.</font> <p><font face="Arial" size="3"><a NAME="const"><b>const</b> </a> <br>A C++ keyword related to the notion of read-only access. An object or reference may be designated as const, to make it clear that it should not be modified within the given context. A member function of a class may also be designated const, to indicate that calling that function will not result in a change in the object s state, and therefore that that function may be called for a const object.</font> <p><font face="Arial" size="3"><a NAME="constructor"></a><b>Constructor</b> <br>A special member function of a class, used to create and initialize objects of that class.</font> <p><font face="Arial" size="3"><a NAME="cpp_file"></a><b>.<a name="cpp file">cpp file</a></b> <br>A C++ source code file.</font> <p><font face="Arial" size="3"><a NAME="cpp_file_runset"></a><b>.<a name="cpp file (for a run set)">cpp file (for a run set)</a></b> <br>A C++ source code file containing the main program for a run set, with a name of the form &lt;system class name>+"Run"+&lt;run set name>+".cpp".</font> <p><font face="Arial" size="3"><a NAME="cpp_file_systemclass"></a><b>.<a name="cpp file (for a system class)">cpp file (for a system class)</a></b> <br>A C++ source code file sometimes used to store the functions defining the behavior of a system class, named the same as the system class, but with the extension ".cpp". A .cpp file is used only in cases where the .h file has been modified by hand, and only when the system class designer chooses to do so, in order to permit separate compilation.</font> <p><font face="Arial" size="3"><a NAME="data_member"></a><b><a name="Data member">Data member</a></b> <br>An object (or variable) that constitutes part of the state information for a given class. A class may have any number of data members, each with its own unique name, and each may be of any legal C++ type. Ordinary (non-static) data members are used to store data related to one specific object of the class, and are accessed using a  dotted" notation, as shown: myObject.myDataMember. Static data members are used to store data shared among all objects of the class, and are accessed using the class name followed by a double colon, as follows: MyClass::myStaticDataMember.</font> <p><font face="Arial" size="3"><a NAME="deep_copy"></a><b><a name="Deep copy">Deep copy</a></b> <br>A copy operation performed on a usage instance of a class, that involves copying not only the instance information, but also the class itself, and also any other classes needed by that class. For example whenever the user cuts and pastes a subsystem from a <i>work directory</i> to any other directory (another work directory or a <i>library directory</i>), a deep copy is performed: all the classes for the subsystem, its subsystems, and so forth found in the source directory are copied to the destination directory. Classes from library directories are not copied however, as they should still be accessible from the destination directory. See also <i>shallow copy</i>.</font> <p><font face="Arial" size="3"><a NAME="default_value"></a><b><a name="Default value (for input or parameter)">Default value (for input or parameter)</a></b> <br>A <i>setting expression</i> provided by the designer of a system class to be used to set the value of an input to that class in case that input is not connected and no other setting expression has been provided. The expression is evaluated in the scope of the containing class, so the only way to ensure that it will be valid is to use either no symbols at all, e.g. a numerical consant, or only symbols defined in the user-provided C++ code. Alternately, the designer may choose to use symbols in the default expression, and rely on the automatic error-checking mechanisms to inform the user about the undefined symbols, which he may then choose to make parameters of the containing system class.</font> <p><font face="Arial" size="3"><a NAME="derived_class"><b>Derived class</b> </a> <br>A class that is derived from another less specialized class, its base class, which defines a portion of the interface and/or implementation of the derived class. See also <i>derived class</i>.</font> <p><font face="Arial" size="3"><a NAME="destructor"></a><b>Destructor</b> <br>A special member function for a class, called when an object of that class is to be removed from memory, and typically used to perform any necessary cleanup, such as freeing dynamically allocated memory.</font><p style="word-spacing: 0; margin-left: -2; margin-right: 0; margin-top: 0; margin-bottom: 0">&nbsp;<p style="word-spacing: 0; margin-left: -2; margin-right: 0; margin-top: 0; margin-bottom: 0"><font face="Arial" size="3"><a NAME="double"></a><b><a name="double &nbsp;(C++ intrinsic type)">double <span style="mso-spacerun: yes"></span>(C++ intrinsic type)</a></b></font> <p class=MsoNormal style="word-spacing: 0; margin-left: -2; margin-right: 0; margin-top: 0; margin-bottom: 0"><font size="3" face="Arial">double is a C++ intrinsic type used to represent real-valued numbers, similar to float, but with greater precision and range.</font></p> <p><font face="Arial" size="3"><a NAME="event"></a><b>Event</b> <br>Events are used in modeling discrete transitions in a system s state caused by its internal time dependence. Generally each system which undergoes such transitions schedule events for itself, and only for itself, using the method scheduleEvent(). Each call to scheduleEvent() results in a delayed call-back to the virtual method respondToScheduledEvent(), unless it is cancelled before, using cancelEvent(). Each event has a character string descriptor, used to distinguish between different types of state transitions, and a void* pointer which can be used to attach information pertaining to the event. For example in modeling a packet-based communications system the pointer might be used to attach the contents of a message packet.</font> <p><font face="Arial" size="3"><a NAME="event_queue"></a><b><a name="Event queue">Event queue</a></b> <br>A data structure containing all pending events for all systems within a given virtual universe, in order of their scheduled execution times. The simulation progresses, and virtual time advances, as events are pulled off the front of the queue and executed; this happens within advanceTime(). Events can be placed on the queue using scheduleEvent(), and removed from the queue using <i>cancelEvent()</i>.</font> <p><font face="Arial" size="3"><a NAME="eventid"></a><b><a name="EventId (C++ class)">EventId (C++ class)</a></b> <br>An object used to identify a specific event, which can be used for the purpose of canceling that event. Each call to scheduleEvent() returns an EventId, and cancelEvent() takes an EventId as an argument.</font> <p><font face="Arial" size="3"><a NAME="external_input"></a><b><a name="External input">External input</a></b> <br>An input to a system or system class; the adjective "external" is sometimes used to make it clear we are referring to an input of the system, rather than an input of one of its subsystems.</font> <p><font face="Arial" size="3"><a NAME="external_output"></a><b><a name="External output">External output</a></b> <br>An output of a system or system class; the adjective "external" is sometimes used to make it clear we are referring to an output of the system, rather than an output of one of its subsystems.</font> <p><font face="Arial" size="3"><a NAME="for_loop"></a><b><a name="For-loop">For-loop</a></b> <br>A loop that repeats the same sequence of comands until a specified condition is met. Typically a for-loop has a <i>loop variable</i>, and integer variable which starts at zero and increments with each iteration of the loop, and exit condition is met when that counter reaches a specified number.</font> <p style="word-spacing: 0; margin: 0">&nbsp; <p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="float"><b>float<span style="mso-spacerun: yes"></span>(C++ intrinsic type)</b></a></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">float is a C++ intrinsic type used to represent real-valued numbers.</font></p> <p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="Grid"><b>Grid&lt;T&gt; <span style="mso-spacerun: yes"></span>(C++ template class)</b></a></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">Grid is a C++ template class, part of the tempus support libraries, used to define a two-dimensional rectangular grid over a specific rectangular region on a plane.<span style="mso-spacerun: yes"> </span>A Gird&lt;float&gt; can be used to define a real-valued function over such a region, e.g. light intensity, while a Grid&lt;float&gt; can be used to define a complex-valued function, such as a complex field.<span style="mso-spacerun: yes"> </span>Grid is used extensively in WaveTrain, both internally, and at the user interface level, where parameters of type Grid can be used to specify things like reflectance maps and detector responsivities.</font></p> <p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="GridGeometry"></a><b><a name="GridGeometry &nbsp;(C++ class)">GridGeometry <span style="mso-spacerun: yes"></span>(C++ class)</a></b></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">GridGeometry is a C++ class, part of the tempus support libraries, used to define the geometry of a two-dimensional rectangular grid over a specific rectangular region on a plane.<span style="mso-spacerun: yes"> </span>GridGeometry is used to specify the geometry for instances of the template class <b>Grid</b>, which is used extensively in WaveTrain, to describe things like optical wavefronts, reflectance maps and detector responsivities.</font></p> <p><font face="Arial" size="3"><a NAME="h_file"></a><b><a name=".h file">.h file</a></b> <br>See <i>header file</i>.</font> <p><font face="Arial" size="3"><a NAME="h_file_systemclass"></a><b><a name=".h file (for a system class)">.h file (for a system class)</a></b> <br>A C++ header file which contains the source code definition for a system class, named the same as the system class, but with the extension ".cpp". The .h file may be entirely automatically generated  generally the case for composite system classes  or it may be modified by hand  generally the case for atomic system classes. When a .h file has been hand-modified, and is later automatically regenerated, e.g. when the user modifys the interface in the visual editor then does a "save", the obsolete hand-modified version is automatically appended to the new generated version, for use in cutting and pasting.</font> <p><font face="Arial" size="3"><a NAME="hard_real_time"></a><b><a name="Hard real-time">Hard real-time</a></b> <br>A hard real-time application is one in which strict and precise time constraints apply, and failure to meet those constraints would result in unacceptable consequences. A typical example would be an automated control loop for a weapons system.</font> <p><font face="Arial" size="3"><a NAME="hasChanged"><b>hasChanged()</b> </a> <br>A method of class Input, used by a system to check whether the value of a particular Input has changed since the last call to respondToChangedInputs(). hasChanged() takes no arguments, and returns a bool. It is typically called within respondToChangedInputs(), to determine which inputs have changed, and which have not.</font> <p><font face="Arial" size="3"><a NAME="header_file"></a><b><a name="Header file">Header file</a></b> <br>A source code file, typically with the extension ".h", intended to be included into other source code files, both .h and .cpp. One common use is define constants used in multiple places; another is to define the interface for one or more classes and/or global functions, but often not the actual implementation, which instead is put into a separate .cpp file, so that it may be compiled separately.</font> <p><font face="Arial" size="3"><a NAME="html_file"><b>.html file (for a system class)</b> </a> <br>A hypertext help file for the system class, named the same as the system class, but with the extension ".cpp". A simple version is generated automatically, listing inputs, outputs, parameters, and subsystems, and so forth; additional text can be added by hand as desired.</font> <p><font face="Arial" size="3"><a NAME="include_file"><b>Include file</b> </a> <br>See <i>header file</i>.</font> <p><font face="Arial" size="3"><a NAME="include_statement"></a><b>Include statement</b> <br>A C++ precompiler directive, used to indicated that the source code from a specified <i>header file</i> should be included into that of the present file, at the site of the include statement, prior to compilation. This mechanism is used to introduce definitions for classes, functions, and/or constants to be used later in the present file.</font> <p><font face="Arial" size="3"><a NAME="inheritance"></a><b>Inheritance</b> <br>One of the key concepts of object-oriented programming (OOP), inheritance is the mechanism by which one class, a <i>derived class</i>, can derive part of its interface and/or implementation from another, its <i>base class</i>. The derived class inherits all the data members and member functions of its base class, and may add its own. Also, a base class may define <i>virtual methods</i>, used to provide a common external interface to all derived classes, while permitting their specific behaviors to differ.</font> <p><font face="Arial" size="3"><a NAME="Input"></a><b>Input</b> <br>A part of the external interface of a system or system class, used to define how a system s environment can act upon the system. An input is a <i>proxy object</i>, an object which "stands for" some other object, typically an output from some other system. An input provides only read-only access to the referent object. This relationship is established by <i>connecting</i> the input to the output, using one of the operators &lt;&lt;= or =>>. Each input must be connected to exactly one output, unless a default value has been provided, in which case it need not be connected. A system may have any number of inputs, and each has a name (a character string, which must be a legal C++ variable name) and a type (any C++ type, including user-defined types). A system is automatically notified each time any of its inputs may be about to undergo a discrete state transition, such as a change of value, via a call to the virtual method respondToInputWarning(), and receives a second notice after the transition has occurred via a call to the virtual method respondToChangedInputs(). Also, whenever a system tries to access the value of one of its inputs, the system with the connected output is notified via a call to the virtual method respondToOutputRequest().</font> <p><font face="Arial" size="3"><a NAME="input_cpp_class"><b>Input (C++ class)</b> </a> <br>Part of the tempus kernel library, Input is a C++ template class used to represent system inputs.</font> <p>&nbsp; <p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="int"></a><b><a name="int &nbsp;(C++ intrinsic type)">int <span style="mso-spacerun: yes"></span>(C++ intrinsic type)</a></b></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">int is a C++ intrinsic type used to represent integer-valued numbers.</font></p> <p><font face="Arial" size="3"><a NAME="instance_of_a_class"><b>Instance (of a class)</b> </a> <br>Generally, the term "instance" refers to a specific object of the class, resident in memory. Sometimes the term is also used to refer to a specific variable of the class type, such as a data member of a class, even when that same variable may represent multiple actual objects. For each (non-static) data member of a class, there are as many actual objects as there were instances of the class. We sometimes refer to the latter case as a <i>usage instance</i>, to distinguish it from the first.</font> <p><font face="Arial" size="3"><a NAME="library"><b>Library (or library directory)</b> </a> <br>A directory used to store tempus system classes intended for reuse. To designate a directory to be a library, one puts a text file named "tempus_resources" in the directory, containing the line "IS_LIBRARY=TRUE"; any directory containing tempus system classes and not so designated is considered a "work directory". The distinction between the two is that in a work directory it is assumed that the user is trying to use tempus as a tool, to solve a problem, whereas a library directory is used to extend the capabilities of tempus, by providing a set of reusable and mutually compatible components. In a work directory the user typically makes frequent changes to his system classes, as he develops and refines his overall system model or models, so it would not make sense to use those same system classes as subsystems in unrelated models. In contrast, system classes in a library directory are intended for reuse and designed for it, and may be used as subsystems in any number of work directories. This difference is reflected in tempus copy mechanism: when one copies a subsystem from a system class in a library directory into a system class in another directory, a <i>shallow copy</i> is performed; which introduces a dependence between the destination directory and the library directory. When one copies a subsystem from a system class in a work directory into a system class in another directory, a <i>deep copy</i> is performed, and no such dependence is introduced.</font> <p><font face="Arial" size="3"><a NAME="lazy_evaluation"></a><b><a name="Lazy evaluation">Lazy evaluation</a></b> <br>The strategy of waiting until the results of a computation are needed before performing the computation, as opposed to, for example, computing it as soon as new inputs value become available. This strategy is especially useful when the inputs may change more often than the results are needed, and each computation costs appreciable cpu-time.</font> <p><font face="Arial" size="3"><a NAME="legal_variable_name_cpp"></a><b><a name="Legal variable name (in C++)">Legal variable name (in C++)</a></b> <br>Legal variable names in C++ may be up to 255 characters long, consisting of letters, numerals, and underscores, and must begin with a letter or underscore. Variable names cannot be the same as C++ keywords, or the same as other variable names in the namespace. C++ is case-sensitive.</font> <p><font face="Arial" size="3"><a NAME="loop_variable"></a><b><a name="Loop variable">Loop variable</a></b> <br>An integer variable, used in conjunction with a <i>for-loop</i>, which starts at zero and increments with each iteration of the loop, and exit condition is met when that counter reaches a specified number.</font> <p><font face="Arial" size="3"><a NAME="loop_variable_runset"></a><b><a name="Loop variable (in a run set)">Loop variable (in a run set)</a></b> <br>Loop variables are a special type of <i>run variable</i>, used to define a set of nested for-loops within a <i>run set</i>, while the actual simulation runs would take place inside the innermost loop. To add a for-loop in the Run Set Edit window, one simply adds a new run variable, say iloop, and sets its type to int and its value to $loop(<i>niter</i>), where <i>niter</i> specifies the number of loop iterations. In the generated source code this would appear as follows, where we have set <i>niter</i> equal to 3:</font> <p><font face="Arial" size="3">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; for (iloop=0; iloop&lt;3; iloop++){& }</font> <p><font face="Arial" size="3">Generally the reason one would wish to set up a for-loop would be to change the value of one or more system parameters with each iteration of the loop. This is done by setting the value of the parameter to an expression of the form [iloop]:{<i>v1</i>,<i>v2</i>,<i>v3& </i>}, where <i>v1,v2,v3& </i> are the desired values for the parameter, one for each loop iteration, or of the form [iloop]: <i>expression</i>, where <i>expression</i> is any legal C++ expression, generally involving the loop variable. If multiple loop variables are used, the for-loops are nested, with the loop corresponding to the first loop variable outermost. To make a parameter dependent on two or more loop variables, one simply lists them inside the square brackets, separated by commas, as follows: [iloop,jloop,kloop] The total number of runs in the run set is given by the product of the numbers of iterations for all loop variables.</font> <p><font face="Arial" size="3"><a NAME="member_function"></a><b><a name="Member function">Member function</a></b> <br>A function associated with a particular class that defines part of the interface and behavior of that class. Ordinary (non-static) member functions define operations that effect one specific object of the class, and are invoked using a  dotted" notation, as shown: myObject.myMemberFunction(). Static member functions define operations not necessarily related to any specific object of the class, such as operations that involve static <i>data members</i> of the class, and are invoked using the class name followed by a double colon, as follows: MyClass::myStaticMemberFunction()</font> <p><font face="Arial" size="3"><a NAME="method"><b>Method</b> </a> <br>A synonym for <i>member function</i>.</font> <p><font face="Arial" size="3"><a NAME="mutable_input"><b>MutableInput (C++ class)</b> </a> <br>Similar to an ordinary input, except that it provides full read-write access to the referent object. A mutableInput cannot be connected to an ordinary output; instead they can only be connected to a <i>mutableOutput</i> or an <i>object</i>, both of which support read-write access. See also <i>Input</i>, <i>Input (the C++ class).</i> </font> <p><font face="Arial" size="3"><a NAME="mutable_output"></a><b><a name="MutableOutput (C++ class)">MutableOutput (C++ class)</a></b> </font> <p><font face="Arial" size="3">Similar to an ordinary output, except it permits full read-write access to its referencors. A mutableOutput may be connected to ordinary inputs, mutableInputs, or both. See also <i>Output</i>,<i> Output (the C++ class)</i>.</font> <p><font face="Arial" size="3"><a NAME="now"></a><b><a name="now()">now()</a></b> <br><b>now()</b> is a member function of class System which returns the current virtual time. It takes no arguments.</font> <p><font face="Arial" size="3"><a NAME="object"><b>Object</b> </a> <br>One of the key concepts of object-oriented programming (OOP), an OOP object is analogous to a real world object, in that objects can be created and destroyed, and each object has its own state information, which can evolve over time, in accordance with specified behavioral rules. In C++ each object is an instance of some <i>class</i>, and it is the class that defines the nature of the state information, in the form of <i>data members</i>, and behavior, in the form of <i>member functions</i>.</font> <p><font face="Arial" size="3"><a NAME="object_cpp"></a><b><a name="Object (C++ class)">Object (C++ class)</a></b> <br>Part of the tempus kernel library, Object is a template class which defines a simple kind of <i>proxy object</i>, a wrapper for an object of arbitrary type which can serve as the referent for any number of system inputs. Any action which would modify the state/value of the underlying object is automatically trapped, and any systems with attached inputs are called with respondToInputWarning().</font> <p><font face="Arial" size="3"><a NAME="object_method"><b>object()</b> </a> <br>A member function of Output that returns a non-const reference to the underlying object. The result is equivalent to that of the dereference operator (*), or to implicit or explicit type conversion (to the type of the underlying object), but using the explicit function call can make the code more readable. Any systems with attached inputs are automatically called with respondToInputWarning(). In logic that requires repeated access to an output s underlying object we recommend calling object() once, to initialize a reference, then using the reference for all subsequent accesses.</font> <p><font face="Arial" size="3"><a NAME="object-oriented programming"></a><b>Object-oriented programming</b> <br>A programming paradigm based on the concepts of <i>objects</i> and <i>classes</i>, as opposed to procedures. Many developers find that object-oriented programming, or OOP, conforms much more closely to the way they naturally think about problem solving and design.</font><p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><b><font face="Arial" size="3"><a NAME="object-oriented software composition">Object-oriented software composition</a></font></b> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">Object-oriented software composition, component-based software, is an approach for extending traditional object-oriented programming techniques for very large projects, and/or projects which involve the combined use of many separately designed and developed software components.<span style="mso-spacerun: yes"> </span>The essential idea is to adopt an architecture and methodology which allows the programmer to treat software components more or less like  black boxes , which he can connect together to accomplish the desired purpose without detailed knowledge of their inner workings.</font></p> <p><font face="Arial" size="3"><a NAME="oop"></a><b>OOP</b> <br>An acronym for <i>object-oriented programming.</i> </font> <p><font face="Arial" size="3"><a NAME="Output"></a><b>Output</b> <br>A part of the external interface of a system or system class, used to define how a system can act upon its environment. An output is essentially a wrapper for an underlying object, which can be of any C++ type, where the output can be used as the referent for one or more inputs of that same type. This relationship is established by <i>connecting</i> the input to the output, using one of the operators &lt;&lt;= or =>>. A system may have any number of outputs, and each has a name (a character string, which must be a legal C++ variable name) and a type (any C++ type, including user-defined types). A system is automatically notified each time any of its outputs is about to be accessed through a connected input, via a call to the virtual method respondToOutputRequest. Also, whenever a system attempts to modify an output, e.g. in an assignment statement, all systems with connected inputs are automatically warned, via calls to the virtual method respondToInputWarning.</font> <p><font face="Arial" size="3"><a NAME="output_cpp"></a><b><a name="Output (C++ class)">Output (C++ class)</a></b> <br>Part of the tempus kernel library, Output is a C++ template class used to represent system outputs.</font> <p><font face="Arial" size="3"><a NAME="Parameter"></a><b>Parameter</b> <br>Parameters are variables used to fine-tune the behavior of each instance of a particular system class, and/or to define its initial conditions; at the source code level, parameters appear as constructor arguments. A system class may have any number of parameters, and each has a name (a character string, which must be a legal C++ variable name) and a type (any C++ type, including user-defined types). When an instance of a system class appears as a subsystem within another system class, its parameter values are specified by <i>setting expressions</i> defined in terms of the parameters of the containing system class. When a system class serves as the basis of a <i>run set</i>, its parameter values are specified by setting expressions defined in terms of the <i>run variables</i> defined for the run set. Typically the run variables would include one or more <i>loop variables</i>, used to set up multiple simulation runs, using different parameter values.</font> <p><font face="Arial" size="3"><a NAME="pendingEvents"><b>pendingEvents</b> </a> <br>A data member of class System, a list of all events the system currently has pending, i.e. scheduled, but not yet executed. For a system that schedules events, this list constitutes an important part of the system s state, and in some cases it may be necessary or useful to make use of the pending events list within the system s <i>respondTo- methods</i>.</font> <p><font face="Arial" size="3"><a NAME="pointer"></a><b>Pointer</b> <br>A simple object that records the address of some other object, of some specified type. Pointers can be used to access the pointed-to object by means of the dereference operator (*) and the member dereference operator (->).</font> <p><font face="Arial" size="3"><a NAME="proxy_object"><b>Proxy object</b> </a> <br>An object used to represent another object, so that actions performed on the proxy object are actually forwarded to the object it represents. A proxy object is similar to a <i>reference</i>, but unlike a reference, it is a first class object, defined by a class, with its own data members and member functions. A typical application is to trap attempts to access the represented object, and then perform some appropriate action. Ideally, one should be able to substitute a proxy object for the represented object in any valid expression and get exactly the same result, but unfortunately in C++ this is not possible, because of subtleties related to the rules for automatic type conversion and the member access (.) operator. To get around this, the designers of proxy classes typically define a member function or operator which returns a reference to the underlying object, which can then be used in any expression. In tempus, the proxy classes <i>Input</i>, <i>Output</i>, and <i>SaveVariable</i> provide both, via the dereference operator (*), implicit or explicit type conversion, and the member functions value() (const access) and object() (non-const access, Output and SaveVariable only).</font> <p><font face="Arial" size="3"><a NAME="reference"></a><b>Reference</b> <br>In C++ a reference is similar to a pointer, except that, unlike pointers, references are used syntactically just like the represented object, and are not themselves considered first class objects, in that once a reference has been defined no further action can be performed on it, since all actions are forwarded to the referred-to object.</font> <p><font face="Arial" size="3"><a NAME="Recallable"></a><b><a name="Recallable (C++ class)">Recallable (C++ class)</a></b> <br>A recallable is a variable whose value may change with the advance of virtual time, and for which it is possible to recall its value at earlier virtual times by calling <i>valueAt()</i>, a member function which takes a single argument, the time for which the value is desired. Recallables are generally used only when there is reason to expect that it will be necessary to access values from earlier times, as is the case for subsystems used to drive others which rely on being able to access their inputs at earlier times. Recallable is a template class (Recallable&lt;T>), where the template argument is the variable type. See also <i>recallRecallable</i>, <i>SaveVariable</i>.</font> <p><font face="Arial" size="3"><a NAME="recallRecallable"></a><b><a name="recallRecallable()">recallRecallable()</a></b> <br>A virtual method of class System, used only in systems which make use of <i>recallables</i>, either in their internal logic, or as outputs. recallRecallable takes two arguments, one to identify which recallable, one to specify the virtual time for the recalled value. recallRecallable does not have a return value; instead, the recalled value is stored in a data member of class Recallable&lt;T>, called recalledValue. We do it that way because the recalled values for different recallables have different types. See also <i>Recallable, SaveVariable</i>.</font><p style="word-spacing: 0; margin: 0">&nbsp;<p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="RectangularRegion"></a><b><a name="RectangularRegion &nbsp;(C++ class)">RectangularRegion <span style="mso-spacerun: yes"></span>(C++ class)</a></b></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">RectangularRegion is a C++ class, part of the tempus support libraries, used to define a two-dimensional rectangular region on a plane.<span style="mso-spacerun: yes"> </span>RectangularRegion <span style="mso-spacerun: yes"></span>is closely related to the class GridGeometry, used to specify the geometry for instances of the template class <b>Grid</b>, which is used extensively in WaveTrain, to describe things like optical wavefronts, reflectance maps and detector responsivities.</font></p> <p><font face="Arial" size="3"><a NAME="respondTo methods"><b>respondTo- methods</b> </a> <br>A set of four virtual methods of the class System, used to define the behaviors of all system classes. The four methods  <i>respondToChangedInputs()</i>, <i>respondToInputWarning()</i>, r<i>espondToOutputRequest()</i>, <i>respondToScheduledEvent()</i>  define the system s responses to changes to its inputs, requests for its outputs, and scheduled events.</font> <p><font face="Arial" size="3"><b><a name="respondToChangedInputs()">respondToChangedInputs()</a></b> <a name="respondToChangedInputs()"> <br></a>One of the four <i>respondTo- methods</i> used to define the behavior of a system class, respondToChangedInputs() is called whenever one or more of the system s inputs have changed, after they have assumed their new values, but before virtual time is allowed to advance. It has no arguments. Note that "Inputs" is plural, reflecting the fact that the values of two or more inputs may change at the same virtual time; to find out which ones have changed, the programmer can use <i>hasChanged()</i>, a member function of the class Input.</font> <p><font face="Arial" size="3"><b><a name="respondToInputWarning(0">respondToInputWarning(0</a></b> <br>One of the four <i>respondTo- methods</i> used to define the behavior of a system class, respondToInputWarning() is called whenever any one of the system s inputs is about to change, before it has assumed its new value. There is one argument, which identifies the input. Generally speaking, respondToChangedInputs() should be used in preference to respondToInputWarning(); this allows the programmer to deal with multiple changed inputs at the same time, after their new values are available, and avoids possible deadlock conditions.</font> <p><font face="Arial" size="3"><b><a name="respondToOutputRequest()">respondToOutputRequest()</a></b> <br>One of the four <i>respondTo- methods</i> used to define the behavior of a system class, respondToOutputRequest() is called whenever any one of the system s outputs is about to be accessed. There is one argument, which identifies the output. This gives the programmer the option of adopting a strategy of <i>lazy evaluation</i>, i.e. computing the value of the output only when it is requested. One reason one might choose that strategy is efficiency, especially in the case of outputs whose values may change much more often than they are accessed, and where each output evaluation takes a significant amount of CPU time. Another reason would be if the output models a quantity that may change continuously in time, such as the instantaneous position of a damped harmonic oscillator. By waiting for the output request, we can compute the position for the precisely the right instant in virtual time.</font> <p><font face="Arial" size="3"><b><a name="respondToScheduledEvent()">respondToScheduledEvent()</a></b> <br>One of the four <i>respondTo- methods</i> used to define the behavior of a system class, respondToScheduledEvent() is called whenever an event scheduled by the system reaches the top of the event queue. There are three<b>?????????????? </b>arguments, & .</font> <p><font face="Arial" size="3"><a NAME="Run"></a><b>Run</b> <br>See simulation run.</font> <p><font face="Arial" size="3"><a NAME="run_file"><b>.run file</b> </a> <br>A text file used by the tempus visual editor to store the definition of a run set, named the same as the system class, but with the extension ".cpp". .run files are user-readable, containing the same information displayed in the <i>edit run set window</i>, and can be useful as a form of documentation.</font> <p><font face="Arial" size="3"><a NAME="run_set"><b>Run set</b> </a> <br>A set of simulation runs, all based on the same system class, and generally executed as part of the same main program, but differing in the values used for one or more system parameters. A run set is typically used to perform a specific parameter study based on the given system model, e.g. how does such-and-such performance measure change when one turns some particular knob? For system models that include stochastic effects one of the parameters varied would often be a random number seed, for the purpose Monte Carlo averaging. Run sets can be created and modified using the <i>run set edit window</i>, where the user specifies which parameters are to be varied and what values they should be set to, what values the other parameters should be set to, the simulation stop time, what outputs to record, and so forth. The information pertaining to a run set is stored on disk in a <i>.run file</i>, kept in the same directory as the system class on which the run set is based. See also <i>simulation run</i>, <i>run set edit window</i>, <i>run variable</i>, <i>loop variable</i>, <i>.run file</i>, and <i>.trf file</i>.</font> <p><font face="Arial" size="3"><a NAME="run_set_edit_window"></a><b><a name="Run set edit window">Run set edit window</a></b> <br>One of the two main windows in the tempus visual editor, used to create and modify <i>run</i> <i>sets</i>. To see the window layout, click <i>here</i>. See also<i> run set, simulation run</i>, <i>run variable</i> and <i>loop variable</i>.</font> <p><font face="Arial" size="3"><a NAME="run_variable"></a><b><a name="Run variable">Run variable</a></b> <br>A variable used within a run set for specifying parameter values and/or setting up for-loops over parameters. One application would be to define quantities to be used in multiple setting expressions; another would be to store expensive-to-compute results which can be reused in multiple simulation runs. There is one special type of run variable, called a <i>loop variable</i>, used for setting up for-loops over parameters.</font> <p><font face="Arial" size="3"><a NAME="SaveVariable"></a><b><a name="SaveVariable (C++ class)">SaveVariable (C++ class)</a></b> <br>A type of <i>recallable</i> variable which keeps track of its own past values, rather than relying upon some System to do so. Each time a saveVariable is modified it records the new value and the virtual time, so that later it can recall its value at any past virtual time. SaveVariable provides a convenient mechanism for keeping track of the time history of quantities that can undergo only discrete changes; quantities that can vary continuously should be modeled using the more general <i>recallable</i>/<i>recallRecallable</i> approach. SaveVariable is a template class (SaveVariable&lt;T>) where the template argument is the variable type.</font> <p><font face="Arial" size="3"><a NAME="scheduleEvent"></a><b><a name="scheduleEvent()">scheduleEvent()</a></b> <br>A method of class System used to schedule events, used to trigger discrete changes in a system s state related to its own internal time dependence. ScheduleEvent takes three arguments: the delay (in virtual time) after which the event should occur, a character string descriptor used to distinguish between different types of events, and a void* pointer which can be used to attach information pertaining to the event. ScheduleEvent() returns an <i>EventId</i>, which can be used to cancel the event should that become necessary.</font> <p><font face="Arial" size="3"><b><a name="seedSequence"></a>seedSequence</b><br> A global function provided to tempus users which allows the generation of a deterministic sequence of random number seeds from a single random number seed. tempus is often used for Monte Carlo runs where it is necessary to change the random number seed for each sample. However, it would be inconvenient for the user to explicitly specify the seed to be used for every single case. seedSequence provides a mechanism to set the seed in a deterministic way depending on a single user-specified seed and iteration number. The form of seedSequence is:</font><p><font face="Arial">int seedSequence(const int seed, const int index) {return (seed + (2*index));}</font><p><font face="Arial">seedSequence is usually used in conjunction with a loop variable. Suppose we have loop variable irand. We can run a Monte Carlo study by setting the random number seed for some entity (such as the atmospheric path) to:</font><p><font face="Arial">[irand]:seedSequence(-123456789,irand)</font><p><font face="Arial">On the first iteration the seed -123456789 will be used, on the next -123456787, and so on. This sceme works well in seeding random number generators for which it is unlikely that two numbers, even if they are almost equal, are unlikely to be close to each other in a given random sequence. Some random number generators (in particular, the one in the Intel performance library) do not have this feature so we do not use it.</font><p><font face="Arial">One might ask why we don't use a single random number seed to seed all random number processes throughout the simulation. This has the undesirable feature that it would be difficult to hold one random process constant while allowing another to vary. Also, the actual sequences that were generated would depend on how many numbers were drawn and if we changed the number of numbers slightly we could get significantly different results.</font><p><font face="Arial" size="3"><a NAME="setting_expression"></a><b><a name="Setting expression">Setting expression</a></b> <br>A C++ expression used to specify a value for a parameter, input, or output, which may be as simple as a numerical constant, e.g. "5.0", or as complicated as needed. A system class may specify default values for its own parameters, inputs, and outputs, and may set the values for its subsystems parameters and inputs, which overrides any defaults specified in the subsystem s system classes. Also, run sets use setting expressions to specify the parameter values for the system model used. Setting expressions are evaluated in the scope where the value is needed, and must therefore be valid C++ expressions within that scope. This means that the setting expressions for subsystem parameters and inputs and external outputs can involve only the parameters of the containing system class, or symbols defined in the user-provided <i>C++ code</i> for the class. Default setting expressions for parameters and inputs are likewise evaluated within the containing class, not the class where they were defined. The only way to ensure that a default expression will be valid expressions is to use either no symbols at all, or only symbols defined in the user-provided C++ code. Alternately, one can use symbols in the default expression, and rely on the automatic error-checking mechanisms to inform the user about the undefined symbols, which he may then choose to make parameters of the containing system class.</font> <p><font face="Arial" size="3"><a NAME="shallow_copy"></a><b><a name="Shallow copy">Shallow copy</a></b> <br>A copy operation performed on a usage instance of a class, that involves copying only the instance information, not the class itself. For example whenever the user cuts and pastes a subsystem from a <i>library directory</i> to any other directory (another <i>work directory</i> or a library directory), a shallow copy is performed, creating a new <i>usage instance</i> of the existing class. See also <i>deep copy</i>.</font> <p><font face="Arial" size="3"><a NAME="simulation_run"></a><b><a name="Simulation run">Simulation run</a></b> <br>A single execution of a simulation, generally occurring within the innermost for-loop of a run set main program. A simulation run generally consists of (1) the construction of a new virtual universe, (2) a call to the constructor of the system class on which the run set is based, which each parameter value set as specified in the run set, (3) set up of output recording as specified in the run set, and (4) a call to <i>advanceTime</i>, used to advance virtual time to the stop time specified either in the run set, or on the command line. Simulation runs can also be used in other ways, such as in conjunction with a nonlinear minimization algorithm for design optimization or fitting a model to data, or as part of an interactive training environment.</font> <p><font face="Arial" size="3"><a NAME="soft_real_time"></a><b>Soft real-time</b> <br>A soft real-time application is one in which time constraints apply, but they are not terribly strict, somewhat imprecise, and failure to meet those constraints would not result in unacceptable consequences. A typical example would be an interactive training environment for operators of some complex system.</font> <p><font face="Arial" size="3"><a NAME="Subsystem"><b>Subsystem</b> </a> <br>A system which is used as part of a larger system or system class. Every subsystem is an <i>instance</i> of some system class, with its parameter values defined by <i>setting expressions</i> defined in terms of the parameters of the containing system class, and its inputs and outputs connected to other subsystems and/or external inputs and outputs as specified by the containing system class.</font> <p><font face="Arial" size="3"><a NAME="System"></a><b>System</b> <br>In tempus a system is a C++ object, an instance of a <i>system class</i>, a C++ class derived from the base class System. The class System is designed to be a software representation of the abstract notion of a system, as the term is used in science and engineering, where a system can be just about anything, provided that it has well-defined inside  the system itself - and outside  its environment. Following the methods of systems engineering, any system can be described in terms of its inputs, outputs, internal state, and behavior, where its behavior consists of its response to changes in its inputs and its internal time dependence. The class System is designed for use as a base class for a wide variety of more specialized classes, each representing a specific type of system, with its own particular inputs, outputs, and behavior. These classes, called <i>system classes</i>, can be created and modified using the <i>tempus visual editor</i>. Some, called <i>composite system classes</i>, are made up of simpler systems, called subsystems, connected together. Others, called <i>atomic system classes</i>, contain no other systems. The behaviors of composite systems are defined by the behaviors of their subsystems; the behaviors of atomic systems are defined by source code. All system classes, both atomic and composite, are generally <i>parameterized</i>, meaning that their behaviors and/or initial conditions are defined in terms of a number of <i>parameters</i>, passed in as constructor arguments. A tempus system is simply one instance of some system class, possibly one of many. Any changes to a system class will affect all its instances, unless the user elects to rename the modified class, in which case he can choose which instances will be affected by the changes, and which will not.</font> <p><font face="Arial" size="3"><a NAME="System_cpp"></a><b><a name="System (C++ class)">System (C++ class)</a></b> <br>Part of the tempus kernel library, the class System, which serves as the base class for all tempus system classes,, is designed to be a software representation of the abstract notion of a system, as the term is used in science and engineering. System provides a customizable interface mechanism based on the use of <i>inputs</i> and <i>outputs</i>, instances of the template classes Input&lt;T> and Output&lt;T>, where inputs are used to define the means by which a system s environment can act upon the system, and outputs are used to define the means by which a system can act upon its environment. System has four virtual methods, collectively called the <i>respondTo- methods</i>, which are used to define the behavior of each system class:<a href="#respondTo methods"><i>respondToChangedInputs()</i>, <i>respondToInputWarning()</i>, <i>respondToOutputRequest()</i>, <i>respondToScheduledEvent()</i></a><i>.</i> The default behavior for each is to do nothing, and for composite system classes that generally suffices, while atomic system classes will generally override one or more of the four. For more details consult the <i>tempus Programmer s Manual</i>.</font> <p><font face="Arial" size="3"><a NAME="SystemClass"></a><b><a name="System class">System class</a></b> <br>A class derived from the base class System, and representing a specific type of system, with its own particular inputs, outputs, and behavior. System classes may be&nbsp; <i><a href="#composite_system_class">composite</a></i>, i.e. made up of <a href="#Subsystem">subsystems</a> (instances of other system classes), or <i><a href="#atomic_system_class">atomic</a></i>. The behaviors of composite systems are defined by the behaviors of their subsystems. The behaviors of atomic systems are defined by source code. System classes can be created and modified using the <i><a href="#tempus_visual_editor">tempus visual editor</a></i>, which automatically generates a four files for each, a <i><a href="#tsd_file">.tsd file</a></i>, a <i><a href="#header_file">.h file</a></i>, a <i>.view file</i>, and a <i><a href="#html_file">.html</a> file</i>. <b>Talk about different directories</b>. The two most important of these are the <a href="#tsd_file">.tsd</a> file, which describes the class to the visual editor, and the .h file, which contains its C++ class definition. When the .h file is generated, the <i>respondTo- methods</i> used to define the class s behavior are commented out; to implement a desired behavior the user would edit the .h file by hand, uncomment one or more of the respondTo- methods, then put the appropriate logic in the function bodies. It may also be necessary or useful to add data members, modify the constructor logic, and so forth; any changes that do not affect the external interface are allowed. It is important to remember that a system class may be used in more than one place, that is instances of the class may appear as subsystems in more than one composite system, or more than once within the same composite system, and that any changes to the system class will affect all instances. For more details, consult the <i>tempus Programmer s Manual</i>.</font> <p><font face="Arial" size="3"><a NAME="system_class_edit_window"></a><b><a name="System class edit window">System class edit window</a></b> <br>One of the two main window in the tempus visual editor, the system class edit window is used to edit or view system classes, represented graphically, as block diagrams. The user may open any number of edit windows, each of which shows one system class at a time. The user can cut and paste subsystems, inputs, and outputs between windows, and can rearrange subsystems, make and break connections, and so forth, all by direct manipulation. He can also navigate through a complete hierarchical system model, double-clicking on a subsystem to descend into the corresponding system class, double-clicking on whitespace to ascend to the level above. If two or more edit windows happen to be looking at the same system class, all actions performed in one will also be reflected in the other. There is an undo capability, and automated error-trapping. A status button at the bottom right turns red whenever any errors are detected; clicking on it brings up a detailed report.</font> <p><font face="Arial" size="3"><a NAME="template"></a><b>Template</b> <br>Templates are the C++ version of generic types, used to define classes and functions that can be used with typed objects, where the type matters, but where at least part of the desired behavior can be defined independent of the specific type. Typical examples include multi-object container classes, such as lists, and proxy objects. A template class or function is defined in terms of one or more <i>template arguments</i>, used to represent the unspecified type or types.</font> <p><font face="Arial" size="3"><b><a name="Template argument">Template argument</a></b> <br>An argument used in the definition of a template class or function to represent the unspecified type or types, and/or to convey other information needed at compile time, such as array dimensions. In the definition of a template class or function, the template arguments appear at the top, immediately following the keyword template, and enclosed in angle brackets:</font> <p><font face="Arial" size="3">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; template &lt;class T> Input {& };</font> <p><font face="Arial" size="3">In usage, the template arguments appear immediately after the class or function name, again enclosed in angle brackets.</font> <p><font face="Arial" size="3">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Input&lt;float> u;</font> <p><font face="Arial" size="3">Within the definition of the class or function, a template argument representing a class is used in place of the class name in declarations, type casts and so forth. To refer to an instance of a template class where a template argument is unspecified we typically write "T" in place of the template argument, as in "Input&lt;T>".</font> <p><font face="Arial" size="3"><a NAME="template_class"></a><b><a name="Template class">Template class</a></b> <br>A class defined in terms of one or more template arguments.</font> <p><font face="Arial" size="3"><b><a name="Template function">Template function</a></b> <a name="Template function"> <br></a>A function defined in terms of one or more template arguments.</font> <p><font face="Arial" size="3"><a NAME="tempus"><b>tempus Programmer s Guide</b> </a> <br>An informal how-to guide for all the basic activities involved in the using tempus at the source code level. The guide is designed for ease of use, and is not intended to be completely comprehensive.</font> <p><font face="Arial" size="3"><b><a name="tempus Programmer s Manual">tempus Programmer s Manual</a></b> <br>A comprehensive user s manual guide for all the basic activities involved in the using tempus at the source code level. Our intention is for the manual to eventually cover every detail of every feature, but as tempus is still in active development it will be some time before that is true.</font> <p><font face="Arial" size="3"><b><a name="tempus recorder file">tempus recorder file</a></b> <br>See .<i>trf file</i>.</font> <p><font face="Arial" size="3"><b><a name="tempus User s Guide">tempus User s Guide</a></b> <br>An informal how-to guide for all the basic activities involved in the use of tempus, from installing the software to building system models and performing parameter studies in the tempus visual editor, then looking at the simulation outputs in Matlab. It does not cover use of tempus at the source code level. The guide is designed for ease of use, and is not intended to be completely comprehensive.</font> <p><font face="Arial" size="3"><b><a name="tempus User s Manual">tempus User s Manual</a></b> <br>A comprehensive user s manual for all the basic activities involved in the use of tempus, from installing the software to building system models and performing parameter studies in the tempus visual editor, then looking at the simulation outputs in Matlab. It does not cover use of tempus at the source code level. Our intention is for the manual to eventually cover every detail of every feature, but as tempus is still in active development it will be some time before that is true.</font> <p><font face="Arial" size="3"><a NAME="tempus_visual_editor"><b>tempus visual editor</b> </a> <br>The tempus graphical user interface (GUI), called the "visual editor" because it is a visual programming environment, used to create and modify tempus system classes and run sets.</font> <p><font face="Arial" size="3"><a NAME="trf_file"><b>.trf file</b> </a> <br>A specially formatted random access file used to store tempus simulation output, generated when a run set main program is executed, named the same as the system class, but with the extension ".cpp". The format preserves the structure character of the output data, and support searching and browsing without having to load the contents of the file. "trf" stands for "tempus recorder file". Interfaces have been implemented for accessing and manipulating trf files from C++ , DOS, Unix, and Matlab; these are described in the .<b>trf File User s Manual</b>.</font> <p><font face="Arial" size="3"><a NAME="tsd_file"><b>.tsd file</b> </a> <br>A text file used by the tempus visual editor to store the definition of a system class, named the same as the system class, but with the extension ".cpp". .tsd files are user-readable, containing the same information displayed in the <i>edit system class window</i>, and can be useful as a form of documentation.</font> <p><font face="Arial" size="3"><a NAME="Universe"></a><b><a name="Universe (C++ class)">Universe (C++ class)</a></b> <br>Part of the tempus kernel library, the Universe is a C++ class designed to represent a <i>virtual universe</i>, within which we can construct a system model, then cause virtual time to advance, independent of any other virtual universes and system models within the same process. Often only a single virtual universe is in use at any one time  that s the case in a typical run set  but some applications require multiple virtual universes, such as those that involve models within models.</font> <p><font face="Arial" size="3"><a NAME="usage_instance"></a><b><a name="Usage instance (of a class)">Usage instance (of a class)</a></b> <br>A variable representing an object of a given class, which does not necessarily refer to a single specific object in memory (i.e. an "instance" in the ordinary sense), because which object in memory it refers to depends upon the usage context. For example, if class A has a non-static data member b of class B, there would be one b for each instance of A  possibly many, or zero - so b would be considered a usage instance of B, but not an instance in the ordinary sense.</font> <p><font face="Arial" size="3"><a NAME="user_defined_types"><b>User-defined types</b> </a> <br>Object-oriented programming languages such as C++ allow programmers to define their own data types, which can then be used just as the intrinsic types defined by the language are. The term <i>user-defined type</i> is almost synonymous with the term <i>class</i>, but in C++ there is also a simpler form called a struct, which can be thought of as a class without any member functions and with all data members publicly accessible.</font> <p><font face="Arial" size="3"><a NAME="value"></a><b><a name="value()">value()</a></b> <br>A member function defined for both inputs and outputs, which returns a const reference to the underlying/referent object. In the case of an input, a call to value() triggers a call to respondToOutputRequest() for the system with the connected output. In the case of an output, calling value()is recommended in logic that requires only read-access to the underlying object, because unlike read-write access mechanisms (e.g. calling object() or using implicit type conversion) it does not trigger calls to respondToInputWarning() for systems with connected inputs.</font> <p><font face="Arial" size="3"><a NAME="valueAt"></a><b><a name="valueAt()">valueAt()</a></b> <br>A member function of <i>recallables</i> and <i>saveVariables</i>, used to access the value of the underlying object at some past moment in virtual time.</font> <p style="word-spacing: 0; margin: 0">&nbsp; <p style="word-spacing: 0; margin: 0"><font face="Arial" size="3"><a NAME="Vector"><b>Vector&lt;T&gt; (C++ template class)</b></a></font> <p class=MsoNormal style="word-spacing: 0; margin: 0"><font face="Arial" size="3">Vector is a C++ template class, part of the tempus support libraries, used to describe an ordered set of similar objects. Vector is used extensively in WaveTrain, both internally and at the user interface level, where parameters of type Grid can be used to specify things like phase screen locations and strengths..</font></p> <p><font face="Arial" size="3"><a NAME="virtual_member_function"></a><b><a name="Virtual member function">Virtual member function</a></b> <br>A member function of a class designed for use as a base class, used to define a common interface to all derived classes, while allowing the behaviors of derived classes to differ. The base class may define a default behavior (implementation of the function), which the designer of a derived class may choose to override. If the base class does not provide a default the function is called a "pure virtual function", and each derived class must provide its own implementation.</font> <p><font face="Arial" size="3"><a NAME="virtual_method"></a><b><a name="Virtual method">Virtual method</a></b> <br>See virtual member function.</font> <p><font face="Arial" size="3"><a NAME="virtual_time"></a><b><a name="Virtual time">Virtual time</a></b> <br>Virtual time plays the same role in a computer simulation that real time does in the real world; when a real world system has been correctly modeled, the behavior of the model unfolds as virtual time advances in a manner closely corresponding to the behavior of the actual system in real time. Unlike real time, virtual time is subject to our complete control, so we can ensure that all simulation events occur at exactly the correct times and in the correct sequence, deterministic and repeatable. Depending on the application, the model, and the computer system, virtual time may advance much more slowly than real time, or much more quickly. In some applications, such as interactive training environments, it is desirable for virtual time to advance at the same pace as real time; given sufficient computing power this is generally easy to do in an approximate sense, but impossible to do with exactitude for an arbitrary computer model. For this reason standard virtual time simulation techniques can be applied directly to <i>soft real-time</i> applications, but not necessarily for <i>hard real-time</i> applications. Simulation techniques can be useful in hard real-time applications, but it is then necessary to either restrict the kinds of software components used (e.g fixed time algorithms), or else adopt an architecture that partly decouples the simulation from the control loop proper.</font> <p><font face="Arial" size="3"><a NAME="void"></a><b>Void</b> <br>A C++ keyword used in place of the return type to indicate that a function does not have a return value, and also used in place of the referent type when declaring pointers to objects of unspecified type.</font> <p><font face="Arial" size="3"><a NAME="work_directory"></a><b>Work directory</b> <br>Any directory used to store tempus system classes and run sets, and not specifically designated to be a <i>library directory</i>. The distinction between the two is that in a work directory it is assumed that the user is trying to use tempus as a tool, to solve a problem, whereas a library directory is used to extend the capabilities of tempus, by providing a set of reusable and mutually compatible components. In a work directory the user typically makes frequent changes to his system classes, as he develops and refines his overall system model or models, so it would not make sense to use those same system classes as subsystems in unrelated models. In contrast, system classes in a library directory are intended for reuse and designed for it, and may be used as subsystems in any number of work directories. This difference is reflected in tempus copy mechanism: when one copies a subsystem from a system class in a library directory into a system class in another directory, a <i>shallow copy</i> is performed; which introduces a dependence between the destination directory and the library directory. When one copies a subsystem from a system class in a work directory into a system class in another directory, a <i>deep copy</i> is performed, and no such dependence is introduced.</font> </body> </html>