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function y=logsum(x,d)
%LOGSUM logsum(x,d)=log(sum(exp(x),d))
% d gives dimension to sum along
% Copyright (C) Mike Brookes 1998
%
% Last modified Mon Oct 12 15:47:25 1998
%
% VOICEBOX is a MATLAB toolbox for speech processing. Home page is at
% http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html
%
if nargin==1
d=[find(size(x)-1) 1];
d=d(1);
end
n=size(x,d);
if n<=1, y=x; return; end
s=size(x);
p=[d:ndims(x) 1:d-1];
z=reshape(permute(x,p),n,prod(s)/n);
y=max(z);
y=y+log(sum(exp(z-y(ones(n,1),:))));
s(d)=1;
y=ipermute(reshape(y,s(p)),p);
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