====== catan ======
<code c>
double complex catan(double complex z);
</code>

==== description of catan ====
calculate the complex arc tangent

<code c>
#include <stdio.h>
#include <complex.h>

int main( void )
{

   long double complex zlong=4.2 + I*2.34;
   double complex zdouble=(double complex)zlong;

   double result;

   result = catan(zdouble);
   printf("catan(%f + I*%f) = %f\n", creal(zdouble), cimag(zdouble), result);
   return 0;
}

</code>

===== output of catan c example =====
    catan(4.200000 + I*2.340000) = 1.389300