-
Notifications
You must be signed in to change notification settings - Fork 10
/
cvLogSum.m
46 lines (45 loc) · 1.5 KB
/
cvLogSum.m
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
% cvLogSum - Compute log(sum) of log values
%
% Synopsis
% [logsum] = cvLogSum(A, dim)
%
% Description
% Compute log(sum) of log values, e.g.,
% get log(a + b + c) from log(a), log(b), log(c).
% Useful to take sum of probabilities from log probabilities.
% Useful to avoid loss of precision caused by taking exp.
%
% Inputs ([]s are optional)
% (matrix) A matrix containing log values.
% (scalar) [dim] sums along the dimension dim.
%
% Outputs ([]s are optional)
% (matrix) logsum log(sum) value.
%
% Examples
% >> exp(cvLogSum([log(1) log(2) log(3)]))
% 6
% Authors
% Naotoshi Seo <sonots(at)sonots.com>
%
% License
% The program is free to use for non-commercial academic purposes,
% but for course works, you must understand what is going inside to use.
% The program can be used, modified, or re-distributed for any purposes
% if you or one of your group understand codes (the one must come to
% court if court cases occur.) Please contact the authors if you are
% interested in using the program without meeting the above conditions.
%
% Changes
% 01/01/2009 First Edition
function logsum = cvLogSum(A, dim)
if ~exist('dim', 'var') || isempty(dim), dim = []; end;
% trick to avoid loss of precision as much as possible
if isvector(A) || isempty(dim)
maxval = max(A);
else
maxval = max(A, [], dim);
end
A = A - repmat(maxval, size(A,1)/size(maxval,1), size(A,2)/size(maxval,2));
logsum = log(sum(exp(A), dim)) + maxval;
end