www.pudn.com > 666bandelets_toolbox.zip > l2error.m

function y  = l2error(x) 
% l2error - compute the decreasing of the  
%   L^2 error from orthogonal coefficients. 
% 
%   y  = l2error(x); 
% 
%   y[k]^2 = \sum_{i>=k}{ x~[i]^2 } 
%   where x~ is x sorted in increasing order. 
% 
%   Copyright (c) 2003 Gabriel Peyré 
 
x = reshape(x, prod(size(x)), 1); 
x = rev_sort_abs(x).^2; 
y = sqrt( reverse( cumsum( reverse(x) ) ) );