csinf, csin, csinl

From cppreference.com
< c‎ | numeric‎ | complex
Defined in header <complex.h>
float complex       csinf( float complex z );
(1) (since C99)
double complex      csin( double complex z );
(2) (since C99)
long double complex csinl( long double complex z );
(3) (since C99)
Defined in header <tgmath.h>
#define sin( z )
(4) (since C99)
1-3) Computes the complex sine of z.
4) Type-generic macro: If z has type long double complex, csinl is called. if z has type double complex, csin is called, if z has type float complex, csinf is called. If z is real or integer, then the macro invokes the corresponding real function (sinf, sin, sinl). If z is imaginary, then the macro invokes the corresponding real version of the function sinh, implementing the formula sin(iy) = i sinh(y), and the return type of the macro is imaginary.

Parameters

z - complex argument

Return value

If no errors occur, the complex sine of z.

Errors and special cases are handled as if the operation is implemented by -I * csinh(I*z)

Notes

The sine is an entire function on the complex plane, and has no branch cuts.

Mathematical definition of the sine is sin z =
eiz
-e-iz
2i