function line3d(u)
% Plots the line spanned by u in R^3

	S = meshgrid(-2:.1:2);
	hold on;
		
	X = S*u(1); 
	Y = S*u(2);
	Z = S*u(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');