func GetDiag(arr Arr, submat *Mat, diag int) *Mat {
	mat_new := C.cvGetDiag(
		unsafe.Pointer(arr),
		(*C.CvMat)(submat),
		C.int(diag),
	)
	return (*Mat)(mat_new)
}
func GetDiag(arr Arr, submat *Mat, diag int) *Mat {
	mat_new := C.cvGetDiag(
		unsafe.Pointer(arr),
		(*C.CvMat)(submat),
		C.int(diag),
	)
	return (*Mat)(mat_new)
}
/* Select a diagonal of the input array.
   (diag = 0 means the main diagonal, >0 means a diagonal above the main one,
   <0 - below the main one).
   The diagonal will be represented as a column (nx1 matrix). */