src/thirdparty/mathexpr/example.cpp

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/*

example.cpp , example file for mathexpr.cpp 2.0

Copyright Yann OLLIVIER 1997-2000

This software may be freely distributed as is, including this whole notice.

It may be modified, but any modification should include this whole notice as 
is and a description of the changes made.

This software may not be sold.

This software or any modified version of it may be freely used in free
programs. The program should include a copy of this whole notice.
If you want to use it in a program you sell, contact me

This software comes with absolutely no warranty.

*/

#include <stdio.h>
#include "mathexpr.h"

// Compilation :
// g++ mathexpr.cpp example.cpp -lm
// or
// g++ -c mathexpr.cpp   then   gcc mathexpr.o example.cpp -lm

int main()
{

    // The number that the variable "x" will point to
    float x;
    // Creates a variable named "x" and which value will be x
    RVar xvar ( "x" , &x );

    // Asks for a fomula depending on the variable x, e.g. "sin 2x"
    char s[500]="";
    printf("Enter a formula depending on the variable x:\n");
    gets(s);

    // Creates an operation with this formula. The operation depends on one
    // variable, which is xvar; the third argument is an array of pointers
    // to variables; the previous argument is its size
    RVar* vararray[1]; vararray[0]=&xvar;
    ROperation op ( s, 1, vararray );

    // Affects (indirectly) a value to xvar
    x=3;
    // Printfs the value of the formula for x=3;
    printf("%s = %G for x=3\n\n", op.Expr(), op.Val() );

    // Creates a function name which can be used in later functions to refer to the operation op(x)
    RFunction f (op, &xvar); f.SetName("f");

    // Creates a second variable named y, and a formula depending on both x and y
    float y;
    RVar yvar ( "y" , &y );
    RVar* vararray2[2]; // table of variables containing the adresses of xvar and yvar
    vararray2[0]=&xvar; vararray2[1]=&yvar;

    // Asks for a formula using x, y and the already-defined function f, e.g. x+f(3y)
    printf("Enter a formula using x, y and the function f: x |-> %s that you just entered :\n", op.Expr() );
    gets(s);
    RFunction* funcarray[1]; funcarray[0]=&f;
    ROperation op2 ( (char*)s , 2 , vararray2 , 1, funcarray );
    // vararray2 is a RVar* array with two elements
    // funcarray is a RFunction* array with one element
    y=5;
    printf("Value for x=3, y=5 : %G\n", op2.Val() );

    // Turns the last expression into a function of x and y
    RFunction g(op2, 2, vararray2); g.SetName("g");

    // Here is another way to do it
    float z,t;
    RVar zvar("z", &z), tvar("t", &t);
    ROperation op3,zop,top;
    zop=zvar; top=tvar; // constructs, from a variable, the operation returning its value

    op3=g( (zop+top, top^2) ); // Ready-to-use ; needs two pairs of ( )
    // Now op3 contains the operation op2 with x replaced with z+t, and y replaced with t^2

    z=5;t=7;
    printf("\nLet g be the function g : x,y |-> %s\n", op2.Expr() );
    printf("Value of %s for z=5,t=7:\n %G\n", op3.Expr(), op3.Val() );

    ROperation dopdt = op3.Diff(tvar); // Computes the derivative of op3 w.r.t t
    printf("Value of d/dt (g(z+t,t^2)) = %s for z=5,t=7:\n %G\n", dopdt.Expr(), dopdt.Val() );

    return 0;
}

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