FENIX_libc/math/exp.c

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2022-10-28 04:24:32 +00:00
#include <math.h>
#define TOLERANCE 0.0000001
/*
A C adaptation of Dr. Ching-Kuang Shene's FORTRAN version
from https://pages.mtu.edu/~shene/COURSES/cs201/NOTES/chap04/exp.html
I was stuck on how to actually implement the Taylor series without it
getting far too big for even a long double, and I'm not sure I ever would
have thought to just break it out recursively like this. Instead of each
term being x^n/n!, this says that it's (x/n+1)*(nth term), with a base case
of x/1! = x. Pretty clever, really.
Also, really glad I know how to at least read a basic FORTRAN program. This
probably would have been a little more annoying if I didn't.
-Kat
*/
double exp(double x) {
double term = x;
double sum = 1.0;
for(int i = 1; fabs(term) > TOLERANCE; i++) {
sum += term;
term *= (x / i);
}
return sum;
}