_igam_helper_series Class — pytorch Architecture

Source Code

aten/src/ATen/native/Math.h lines 654–683

template <typename scalar_t>
static scalar_t _igam_helper_series(scalar_t a, scalar_t x) {
  // Compute igam using DLMF 8.11.4. [igam1]
  static scalar_t MACHEP = std::is_same_v<scalar_t, double> ?
    1.11022302462515654042E-16 : 5.9604644775390625E-8;
  static int MAXITER = 2000;

  int i;
  scalar_t ans, ax, c, r;

  ax = _igam_helper_fac(a, x);
  if (ax == 0.0) {
    return 0.0;
  }

  /* power series */
  r = a;
  c = 1.0;
  ans = 1.0;

  for (i = 0; i < MAXITER; i++) {
    r += 1.0;
    c *= x / r;
    ans += c;
    if (c <= MACHEP * ans) {
      break;
    }
  }
  return (ans * ax / a);
}