function [y,c]=ndiff(x,n)
% NDIFF
% [y,c] = ndiff(x,n) differentiates the function in x
% (a column vector or matrix thereof) n times padding
% the end with zeros.  The mean values of each column
% vector before differentiation are returned in the 
% matrix c. (Useful for reconstruction.) 

[i,j]=size(x);
y=x;
c=zeros(i,j);
for m=1:n,
  c(m,:)=mean(y);
  y=diff(y);
end

y=[y;zeros(n,j)];