code: public Vector2d origin(Vector2d origin) {
          double s = 1.0 / (m00 * m11 - m01 * m10);
          origin.x = (m10 * m21 - m20 * m11) * s;
          origin.y = (m20 * m01 - m00 * m21) * s;
          return origin;
      }
docs: Obtain the position that gets transformed to the origin by <code>this</code> matrix.
  This can be used to get the position of the "camera" from a given <i>view</i> transformation matrix.
  <p>
  This method is equivalent to the following code:
  <pre>
  Matrix3x2d inv = new Matrix3x2d(this).invert();
  inv.transform(origin.set(0, 0));
  </pre>
  
  @param origin
  will hold the position transformed to the origin
  @return origin