code: function(theta){
  			var co = Math.cos(theta);
  			var si = Math.sin(theta);
  			var zz = co *this.z - si * this.y;
  			this.y = si * this.z + co * this.y;
  			this.z = zz;
  			return this;
  		}
docs: Rotates the vector by the given angle around the X axis.
  
  @param theta
  the theta
  
  @return itself