code: public void setZero() {
  		xx = 0.0;
  		yx = 0.0;
  		zx = 0.0;
  		xy = 0.0;
  		yy = 0.0;
  		zy = 0.0;
  		xz = 0.0;
  		yz = 0.0;
  		zz = 0.0;
  		xd = 0.0;
  		yd = 0.0;
  		zd = 0.0;
  	}
docs: Sets all elements to 0, thus producing and invalid transformation.