/* ---------------------------------- */
/* save as x_curl.h                      */
/* --------------------------------- */
/*
   with F = Mi + Nj + Pk     

 (curl F) = [(P_y-N_z)i + (M_y-P_z)j + (N_X-M_Y)k]
*/
/* ---------------------------------- */
v3d curl_xyz(
double (*P_M)(double x, double y, double z),
double (*P_N)(double x, double y, double z),
double (*P_P)(double x, double y, double z),
double  h,
p3d p
)
{
v3d  n;

          n.i = fxyz_y((*P_P),h,p) - fxyz_z((*P_N),h,p);
          n.j = fxyz_z((*P_M),h,p) - fxyz_x((*P_P),h,p);
          n.k = fxyz_x((*P_N),h,p) - fxyz_y((*P_M),h,p);

     return(n);
}
/* ---------------------------------- */
/* ---------------------------------- */