Function setmathfuncs 

pub fn setmathfuncs(nam: &str, f: &mut [mathfunc], e: Option<&[i32]>) -> i32

Port of int setmathfuncs(char const *nam, MathFunc f, int size, int *e) from Src/module.c:1374. Bulk add/delete of math-function definitions via the parallel e[] selector array (same shape as setconddefs).