/* makes a star object located uniformly at random within the limits given
on the sphere */
void make_rand_star(double* star, double ramin, double ramax,
double decmin, double decmax)
{
double decval, raval;
if (ramin < 0.0)
ramin = 0.0;
if (ramax > (2*M_PI))
ramax = 2 * M_PI;
if (decmin < -M_PI / 2.0)
decmin = -M_PI / 2.0;
if (decmax > M_PI / 2.0)
decmax = M_PI / 2.0;
decval = asin(uniform_sample(sin(decmin), sin(decmax)));
raval = uniform_sample(ramin, ramax);
star[0] = radec2x(raval, decval);
star[1] = radec2y(raval, decval);
star[2] = radec2z(raval, decval);
}
static double gaussian_sample(double mean, double stddev) {
// from http://www.taygeta.com/random/gaussian.html
// Algorithm by Dr. Everett (Skip) Carter, Jr.
static double y2 = GAUSSIAN_SAMPLE_INVALID;
double x1, x2, w, y1;
// this algorithm generates random samples in pairs; the INVALID
// jibba-jabba stores the second value until the next time the
// function is called.
if (y2 != GAUSSIAN_SAMPLE_INVALID) {
y1 = y2;
y2 = GAUSSIAN_SAMPLE_INVALID;
return mean + y1 * stddev;
}
do {
x1 = uniform_sample(-1, 1);
x2 = uniform_sample(-1, 1);
w = x1 * x1 + x2 * x2;
} while ( w >= 1.0 );
w = sqrt( (-2.0 * log(w)) / w );
y1 = x1 * w;
y2 = x2 * w;
return mean + y1 * stddev;
}
