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Turns out, it only needed to be degree 10!

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Kat R. 2022-10-09 12:09:07 -05:00
parent 664c0d433a
commit a51c11701f
1 changed files with 2 additions and 13 deletions
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15
math/cos.c
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@ -10,14 +10,13 @@
The taylor poly is centered at pi, with a radius of
convergence of no less than pi, making it roughly accurate
between 0 and 2 * pi. The polynomial is up to x^20, so it
should be pretty accurate within that range.
between 0 and 2 * pi. The polynomial is up to x^10, which I've
confirmed as being accurate being 0 and 2 * pi.
*/
double cos(double x) {
double pi = M_PI; /* Really, me?! -Kat */
int temp;
double deg_2, deg_4, deg_6, deg_8, deg_10;
double deg_12, deg_14, deg_16, deg_18, deg_20;
double cosine;
if(x < 0) x = -x;
@ -44,11 +43,6 @@ double cos(double x) {
deg_6 = deg_4 * deg_2 * 2 / (6 * 5);
deg_8 = deg_6 * deg_2 * 2 / (8 * 7);
deg_10 = deg_8 * deg_2 * 2 / (10 * 9);
deg_12 = deg_10 * deg_2 * 2 / (12 * 11);
deg_14 = deg_12 * deg_2 * 2 / (14 * 13);
deg_16 = deg_14 * deg_2 * 2 / (16 * 15);
deg_18 = deg_16 * deg_2 * 2 / (18 * 17);
deg_20 = deg_18 * deg_2 * 2 / (20 * 19);
/*
In case you aren't familiar with the theory of a Taylor
@ -79,13 +73,8 @@ double cos(double x) {
Plus, since we're taking advantage of cosine being an
even function, we don't need any terms less than 0, so
why *center* at zero and include negatives?
(Of course, I've not done the radius of convergence work
for this to find out how many degrees we need to get a
radius of convergence of pi, so I may have used too many
terms, anyways. Not that I can't reduce that...)
*/
cosine = -1 + deg_2 - deg_4 + deg_6 - deg_8 + deg_10;
cosine = cosine - deg_12 + deg_14 - deg_16 + deg_18 + deg_20;
return cosine;
}