code: public boolean isIdentity(double tol) {
  		Point2D pt = Point2D.construct(0., 1.);
  		transform(pt, pt);
  		pt.sub(Point2D.construct(0., 1.));
  		if (pt.sqrLength() > tol * tol)
  			return false;
  
  		pt.setCoords(0, 0);
  		transform(pt, pt);
  		if (pt.sqrLength() > tol * tol)
  			return false;
  
  		pt.setCoords(1.0, 0.0);
  		transform(pt, pt);
  		pt.sub(Point2D.construct(1.0, 0.0));
  		return pt.sqrLength() <= tol * tol;
  	}
docs: Returns TRUE if this matrix is an identity matrix within the given
  tolerance.
  
  @param tol
  The tolerance value.