How Can I Solve NaN Output Problem
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Hı, ı have a code P(i,j) is float and it has value 0-1 range , normally if we calculate log function must be equal positive value with initial minus. But this return to NaN what is the wrong
function entropy=ent(glcm)
P=glcm/sum(glcm(:));
entropy=0;
for i=1:8
for j=1:8
entropy=entropy+ P(i,j)*(-log(P(i,j));
end
end
end
3 Comments
Roger J
on 21 Jul 2020
What is the input to the function?
If glcm matrix is all zeros, then the sum is zero, and that creates NaN in P, and finally the returned entropy is NaN.
Also, don't name the variable "entropy", there is a common function named entropy(..).
Answers (1)
Steven Lord
on 22 Jul 2020
As Roger Jestes stated, if any element of P is exactly 0, you compute 0*(-log(0)) which is 0*inf which results in a NaN. This is the second of the indeterminant forms listed in this section of the Wikipedia page for NaN.
>> 0*(-log(0))
ans =
NaN
NaN plus anything is still NaN so once you add NaN to your entropy value once that's what it will remain.
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