function plane3d(v,w)
% Plots the plane spanned by v and w in R^3

	[S,T] = meshgrid(-2:.1:2); 
	hold on;
		
	X = S*v(1) + T*w(1); 
	Y = S*v(2) + T*w(2); 
	Z = S*v(3) + T*w(3); 
	C = sqrt(X.^2 + Y.^2 + Z.^2);
	M = max(max(C));

	surf(X, Y, Z, C);
	grid on;
	axis([-M M -M M -M M]);
	xlabel('x');
	ylabel('y');
	zlabel('z');