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5 Date started: August 25 2004
7 ------------- Copyright (C) 2001 Jon S. Berndt (jsb@hal-pc.org) -------------
9 This program is free software; you can redistribute it and/or modify it under
10 the terms of the GNU Lesser General Public License as published by the Free Software
11 Foundation; either version 2 of the License, or (at your option) any later
14 This program is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
16 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
19 You should have received a copy of the GNU Lesser General Public License along with
20 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
21 Place - Suite 330, Boston, MA 02111-1307, USA.
23 Further information about the GNU Lesser General Public License can also be found on
24 the world wide web at http://www.gnu.org.
26 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
33 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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39 #include "FGParameter.h"
40 #include <input_output/FGXMLElement.h>
41 #include <input_output/FGPropertyManager.h>
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45 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
47 #define ID_FUNCTION "$Id$"
49 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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55 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
57 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
59 /** Represents a mathematical function.
60 The FGFunction class is a powerful and versatile resource that allows
61 algebraic functions to be defined in a JSBSim configuration file. It is
62 similar in concept to MathML (Mathematical Markup Language, www.w3.org/Math/),
63 but simpler and more terse.
64 A function definition consists of an operation, a value, a table, or a property
65 (which evaluates to a value). The currently supported operations are:
67 - difference (takes n args)
68 - product (takes n args)
69 - quotient (takes 2 args)
79 - atan2 (takes 2 args)
81 An operation is defined in the configuration file as in the following example:
85 <value> 3.14159 </value>
86 <property> velocities/qbar </property>
88 <value> 0.125 </value>
89 <property> metrics/wingarea </property>
94 A full function definition, such as is used in the aerodynamics section of a
95 configuration file includes the function element, and other elements. It should
96 be noted that there can be only one non-optional (non-documentation) element -
97 that is, one operation element - in the top-level function definition.
98 Multiple value and/or property elements cannot be immediate child
99 members of the function element. Almost always, the first operation within the
100 function element will be a product or sum. For example:
103 <function name="aero/coefficient/Clr">
104 <description>Roll moment due to yaw rate</description>
106 <property>aero/qbar-area</property>
107 <property>metrics/bw-ft</property>
108 <property>aero/bi2vel</property>
109 <property>velocities/r-aero-rad_sec</property>
111 <independentVar>aero/alpha-rad</independentVar>
121 The "lowest level" in a function is always a value or a property, which cannot
122 itself contain another element. As shown, operations can contain values,
123 properties, tables, or other operations. In the first above example, the sum
124 element contains all three. What is evaluated is written algebraically as:
126 @code 3.14159 + qbar + (0.125 * wingarea) @endcode
128 Some operations can take only a single argument. That argument, however, can be
129 an operation (such as sum) which can contain other items. The point to keep in
130 mind is that it evaluates to a single value - which is just what the trigonometric
131 functions require (except atan2, which takes two arguments).
136 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
137 DECLARATION: FGFunction
138 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
140 class FGFunction : public FGParameter
145 When this constructor is called, the XML element pointed to in memory by the
146 element argument is traversed. If other FGParameter-derived objects (values,
147 functions, properties, or tables) are encountered, this instance of the
148 FGFunction object will store a pointer to the found object and pass the relevant
149 Element pointer to the constructor for the new object. In other words, each
150 FGFunction object maintains a list of "child" FGParameter-derived objects which
151 in turn may each contain its own list, and so on. At runtime, each object
152 evaluates its child parameters, which each may have its own child parameters to
154 @param PropertyManager a pointer to the property manager instance.
155 @param element a pointer to the Element object containing the function definition.
156 @param prefix an optional prefix to prepend to the name given to the property
157 that represents this function (if given).
159 FGFunction(FGPropertyManager* PropertyManager, Element* element, string prefix="");
161 virtual ~FGFunction();
163 /** Retrieves the value of the function object.
164 @return the total value of the function. */
165 double GetValue(void) const;
167 /** The value that the function evaluates to, as a string.
168 @return the value of the function as a string. */
169 string GetValueAsString(void) const;
171 /// Retrieves the name of the function.
172 string GetName(void) const {return Name;}
174 /** Specifies whether to cache the value of the function, so it is calculated only
176 If shouldCache is true, then the value of the function is calculated, and
177 a flag is set so further calculations done this frame will use the cached value.
178 In order to turn off caching, cacheValue must be called with a false argument.
179 @param shouldCache specifies whether the function should cache the computed value. */
180 void cacheValue(bool shouldCache);
183 vector <FGParameter*> Parameters;
184 FGPropertyManager* const PropertyManager;
188 enum functionType {eTopLevel=0, eProduct, eDifference, eSum, eQuotient, ePow,
189 eExp, eAbs, eSin, eCos, eTan, eASin, eACos, eATan, eATan2} Type;
192 void Debug(int from);
195 } // namespace JSBSim