casin, casinf, casinl - complex arc sine
#include <complex.h>
double complex casin(double complex z);
float complex casinf(float complex z);
long double complex casinl(long double complex z);These functions calculate the complex arc sine of z. If
y = casin(z), then z = csin(y). The real part of
y is chosen in the interval [-pi/2,pi/2].
One has:
casin(z) = -i clog(iz + csqrt(1 - z * z))