code: public boolean isDegenerate(double tol) {
  		return Math.abs(xx * yy - yx * xy) <= 2 * tol
  				* (Math.abs(xx * yy) + Math.abs(yx * xy));
  	}
docs: Returns TRUE if this matrix is degenerated (does not have an inverse)
  within the given tolerance.
  
  @param tol
  The tolerance value.