#include <math.h>
/*
 *  Trigometric expansion basis functions.
 */
void TrigExt( double x, double *afunc, unsigned int nfunc )
{
    double pi = 3.14159265358979;
    double two_pi = 2.0 * pi;

    /*
     *  Sidereal day taken from the Astronomical Almanac 1995 (USNO)
     */
    double sidereal_day = 0.99726956634;

    double period = sidereal_day;
    double P0 = two_pi / period;

    /*
     *  Reference to a specific epoch to help minimize roundoff problems.
     */
    double t0 = x;

    double P;
    int factor = 1;
    unsigned int i = 0;

    afunc[i] = 1.0; ++i;
    while( i < nfunc ) {
        P = (double)factor * P0;
        afunc[i] = sin( t0 * P ); ++i;
        afunc[i] = cos( t0 * P ); ++i;
        ++factor;
    }

    return;
}