static double kaiser(double beta, int M, int n)
{
if (M == 1)
return 1.;
if (fabs((double)n / (double)M - 0.5) >= 0.5)
return 0.;
return bessel_I0(beta * sqrt(1. - pow(2. * (double)n / (double)M - 1., 2.)))
/ bessel_I0(beta);
}
real gdisk(real r)
{
real x1 = 0.5 * alpha1 * r, x2 = 0.5 * alpha2 * r, a1, a2;;
if (epsilon1 >= 0.0) /* compute smoothed accel. */
a1 = - mdisk1 * rqbe(alpha1) *
simpson(dgdisk, r, alpha1, epsilon1, 0, KMAX*alpha1, STEP*alpha1);
else /* use exact expression */
a1 = - mdisk1 * rqbe(alpha1) *
r * (bessel_I0(x1) * bessel_K0(x1) - bessel_I1(x1) * bessel_K1(x1)) / 2;
if (epsilon2 >= 0.0)
a2 = - mdisk2 * rqbe(alpha2) *
simpson(dgdisk, r, alpha2, epsilon2, 0, KMAX*alpha2, STEP*alpha2);
else
a2 = - mdisk2 * rqbe(alpha2) *
r * (bessel_I0(x2) * bessel_K0(x2) - bessel_I1(x2) * bessel_K1(x2)) / 2;
return (a1 + a2);
}
