function x = lsqrfact(A,b)
% LSQRFACT   Solve linear least squares by QR factorization.
%
% Input: 
%   A     coefficient matrix (m by n, m>n)
%   b     right-hand side (m by 1)
%
% Output:
%   x     minimizer of || b-Ax ||
%
    [Q, R] = qr(A, 0);     % compressed factorization
    c = Q'*b;
    x = backsub(R, c);                       
end