camir-aes2014: toolboxes/FullBNT-1.0.7/KPMtools/logsumexp.m annotate

first hg version after svn

rev	line source
wolffd@0	1 function s = logsumexp(a, dim)
wolffd@0	2 % Returns log(sum(exp(a),dim)) while avoiding numerical underflow.
wolffd@0	3 % Default is dim = 1 (rows) or dim=2 for a row vector
wolffd@0	4 % logsumexp(a, 2) will sum across columns instead of rows
wolffd@0	5
wolffd@0	6 % Written by Tom Minka, modified by Kevin Murphy
wolffd@0	7
wolffd@0	8 if nargin < 2
wolffd@0	9 dim = 1;
wolffd@0	10 if ndims(a) <= 2 & size(a,1)==1
wolffd@0	11 dim = 2;
wolffd@0	12 end
wolffd@0	13 end
wolffd@0	14
wolffd@0	15 % subtract the largest in each column
wolffd@0	16 [y, i] = max(a,[],dim);
wolffd@0	17 dims = ones(1,ndims(a));
wolffd@0	18 dims(dim) = size(a,dim);
wolffd@0	19 a = a - repmat(y, dims);
wolffd@0	20 s = y + log(sum(exp(a),dim));
wolffd@0	21 %i = find(~finite(y));
wolffd@0	22 %if ~isempty(i)
wolffd@0	23 % s(i) = y(i);
wolffd@0	24 %end

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