code: public Matrix3d scaling(double x, double y, double z) {
          m00 = x;
          m01 = 0.0;
          m02 = 0.0;
          m10 = 0.0;
          m11 = y;
          m12 = 0.0;
          m20 = 0.0;
          m21 = 0.0;
          m22 = z;
          return this;
      }
docs: Set this matrix to be a simple scale matrix.
  
  @param x
  the scale in x
  @param y
  the scale in y
  @param z
  the scale in z
  @return this