simple-squiggle/node_modules/complex.js/examples/gamma.js

32 lines
825 B
JavaScript

/*
* A gamma function implementation based on Lanczos Approximation
* https://en.wikipedia.org/wiki/Lanczos_approximation
*/
var Complex = require('../complex');
var P = [Complex(0.99999999999980993),
Complex(676.5203681218851), Complex(-1259.1392167224028), Complex(771.32342877765313),
Complex(-176.61502916214059), Complex(12.507343278686905), Complex(-0.13857109526572012),
Complex(9.9843695780195716e-6), Complex(1.5056327351493116e-7)];
var SQRT2PI = Complex(Math.sqrt(2 * Math.PI));
function gamma(z) {
z = z.sub(1);
var x = P[0];
var t = z.add(7.5);
for (var i = 1; i < P.length; i++) {
x = x.add(P[i].div(z.add(i)));
}
return SQRT2PI.mul(t.pow(z.add(0.5))).mul(t.neg().exp()).mul(x);
}
var fac = 1;
for (var i = 1; i <= 10; i++) {
console.log(fac, gamma(Complex(i)));
fac *= i;
}