matlab - Entropy of pure split caculated to NaN -

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i have written function calculate entropy of vector each element represents number of elements of class.

function x = entropy(a)     t = sum(a);     t = repmat(t, [1, size(a, 2)]);     x = sum(-a./t .* log2(a./t)); end

e.g: a = [4 0], entropy = -(0/4)*log2(0/4) - (4/4)*log2(4/4)

but above function, entropy nan when split pure because of log2(0), in above example. entropy of pure split should zero.

how should solve problem least effect on performance data large? thanks

i suggest create own log2 function

function res=mylog2(a)    res=log2(a);    res(isinf(res))=0; end

this function, while breaking log2 behaviour, can used in specific example because multiplying result inside of log, making zero. not "mathematically correct", believe that's looking for.


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