Function gmsh_sys::gmshModelGetDerivative

pub unsafe extern "C" fn gmshModelGetDerivative(
    dim: c_int, 
    tag: c_int, 
    parametricCoord: *mut f64, 
    parametricCoord_n: usize, 
    derivatives: *mut *mut f64, 
    derivatives_n: *mut usize, 
    ierr: *mut c_int
)

Evaluate the derivative of the parametrization of the entity of dimension dim and tag tag at the parametric coordinates parametricCoord. Only valid for dim equal to 1 (with parametricCoord containing parametric coordinates on the curve) or 2 (with parametricCoord containing pairs of u, v parametric coordinates on the surface, concatenated: [p1u, p1v, p2u, ...]). For dim equal to 1 return the x, y, z components of the derivative with respect to u [d1ux, d1uy, d1uz, d2ux, ...]; for dim equal to 2 return the x, y, z components of the derivate with respect to u and v: [d1ux, d1uy, d1uz, d1vx, d1vy, d1vz, d2ux, ...].