public void rotateX(double theta){
  Matrix3D tmp=new Matrix3D();
  double c=Math.cos(theta);
  double s=Math.sin(theta);
  tmp.set(1,1,c);
  tmp.set(1,2,-s);
  tmp.set(2,1,s);
  tmp.set(2,2,c);
  preMultiply(tmp);
}

public void rotateX ( double theta ) { Matrix3D tmp = new Matrix3D ( ) ; double c = Math . cos ( theta ) ; double s = Math . sin ( theta ) ; tmp . set ( 1 , 1 , c ) ; tmp . set ( 1 , 2 , - s ) ; tmp . set ( 2 , 1 , s ) ; tmp . set ( 2 , 2 , c ) ; preMultiply ( tmp ) ; }
rotate transformation about the x axis
