Function Interpreter Functions

   

GRAPE contains a simple but easy to use function interpreter. Once you have a function string (e.g. "x*x+sqrt(y)-z*t") you have to precompile it to a t_fun, providing the variable names. This t_fun can be executed fast enough for most purposes.

The interpreter only knows about scalar double values, it recognizes the operators and functions +, -, *, /, ^, (), arccos, arcsin, arctan, cos, cosh, exp, log, sin, sinh, sqrt, tan, tanh and the constant pi.

t_fun *fn_func (char * in, char * varnames)
Precompile the function in. The variable names have to be in order ans space separated in varnames, e.g. "x y z t". In case of an error NULL is returned; use fn_errstr and fn_errpos for diagnostics.

t_fun *fn_delete (t_fun * fn)
Free the compiled code, return NULL.

double fn_eval (t_fun * fn, double * vars)
Evaluate the compiled function code fn. vars has to contain the variable values in order, e.g. vars[0]=x,vars[1]=y,vars[2]=z,vars[3]=g_maintime. The result value is returned.

char *fn_errstr ()
Return an error message in case fn_eval returned NULL.

char *fn_errpos ()
Return the error position in the function string in case fn_eval returned NULL.