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## Functions

The mathematical functions that the expression evaluator knows are in the array Funcs[] (it is an array of structures FUNCTION). This array must be defined by the user. The total number of functions is _NBFONC, which must be set by the user. An array of functions is predefined in the library, it is called Func_interp, and the number of functions defined in Func_interp is contained in the integer _NBFONC0.

The structure FUNCTION is defined as follows

```typedef struct
{
char* name;                    /* Function name                 */
int   args;                    /* Number of arguments to expect */
double  (*func)(double *);     /* Pointer to function           */
} FUNCTION;
```

The first member of the structure FUNCTION is the character string that will be used to call the function. The second member is the number of parameters of the function. It must be between 1 and the constant MAX_F_ARGS defined in interp.h (it is 10). The third member is the name of the function. It must be a function returning a double value, having only one argument : an array of double precision real numbers. In the array Func_interp the usual mathematical functions are used. It is also possible to put other functions found in some libraries of special functions, like cephes for instance, or defined by the user. The array Func_interp looks like this

```FUNCTION        Funcs_interp[] =
{
/* name, funtion to call */
{ "sin",   1,    _I_sin },      /*  0 */
{ "cos",   1,    _I_cos },      /*  1 */
{ "tan",   1,    _I_tan },      /*  2 */
{ "asin",  1,    _I_asin },     /*  3 */
{ "acos",  1,    _I_acos },     /*  4 */
{ "atan",  1,    _I_atan },     /*  5 */
{ "sinh",  1,    _I_sinh },     /*  6 */
{ "cosh",  1,    _I_cosh },     /*  7 */
{ "tanh",  1,    _I_tanh },     /*  8 */
{ "exp",   1,    _I_exp },      /*  9 */
{ "log",   1,    _I_log },      /* 10 */
{ "log10", 1,    _I_log10 },    /* 11 */
{ "sqrt",  1,    _I_sqrt },     /* 12 */
{ "floor", 1,    _I_floor },    /* 13 */
{ "ceil",  1,    _I_ceil },     /* 14 */
{ "abs",   1,    _I_fabs },     /* 15 */
{ "deg",   1,    _I_deg },      /* 16 */
{ 0 }                           /* 18 */
};

int    _NBFONC0=18;
```

The function _I_sin is defined as follows :

```double
_I_sin(double *x)
{
return sin(*x);
}
```

and the other functions in the array are defined in the same way. For instance if the program uses only the predefined array of functions, the main source file would look as follows :

``` ......
FUNCTION *Funcs;

int main(int argc, char *argv[])
{
Funcs = Funcs_interp;
_NBFONC = _NBFONC0;
......
}
```

Next: User defined functions Up: Expression evaluator Previous: Variables   Contents   Index
2009-11-12