function [Y,p]=detrend2(X)
%DETREND2 Remove linear trends from the columns of a matrix
% DETREND2(X) removes the linear trend from each column of the matrix
% X. 
%
% [Y,Z]=DETREND2(X) returns the linearly detrended matrix in Y 
% and the slopes of the trends of the columns of the matrix X in Z.
  
[M,N]=size(X); 

% Compute linear trend for each variable
t=(1:M)';
t=t-mean(t);
for i=1:N
   [P,S]=polyfit(t,X(:,i),1);
   p(i)=P(1);
end

% Remove the linear trends
Y=X-t*p;
if nargout==1,p=[];,end