func (m *Mass) Rotate(R *Matrix3) {
C.dMassRotate((*C.dMass)(m), (*C.dReal)(&R[0]))
}
// Rotate rotates the mass by rot.
func (m *Mass) Rotate(rot Matrix3) {
c := &C.dMass{}
m.toC(c)
C.dMassRotate(c, (*C.dReal)(&rot[0][0]))
m.fromC(c)
}