% Compute a Givens Rotation
function rot = Givens(x)
% compute c and s so that rot = [[c,s];[-s,c]], rot*x = [norm(x,2);0]
% and c^2 + s^2 = 1
r = norm(x,2);
if r==0,
    c=1;s=0;
else
    c=x(1)/r; s=x(2)/r;
end
rot = [[c,s];[-s,c]];