function B = g_trf(A) 

% function B = g_trf(A) 
% Givens transformation of A, 
% based on the first column 

v = A(:,1);
r = norm(v);
sigma = sign(v(1)); 
if sigma == 0; sigma = 1; end; 
c =  sigma*v(1)/r;
s = -sigma*v(2)/r;

B = [c -s; s c] * A;

