function  [m] = mean_nan(M)

% This routine will calculate the mean of the columns of matrix M, by-passing any
% NaNs found in the array

[I K] = size(M);

for k = 1:K
	igd = find(~isnan(M(:,k)));
  	if (length(igd) > 0)
		m(k) = mean(M(igd,k));
	else
		m(k) = nan;
	end
end
