Element-wise power resulting in imaginary values and NAN
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MathN00b
le 23 Jan 2020
Commenté : Walter Roberson
le 25 Jan 2020
I am using element-wise power .^,which for A.^B should yield a matrix with elements A(i,j) raised to the power B(i,j). However, for the simple example:
A = [-1, 0; 0, -1];
B = [1, 0; 0, 1];
A.^B
I'm getting
ans =
-1.0000 + 0.0000i NaN + 0.0000i
NaN + 0.0000i -1.0000 + 0.0000i
If I use a loop, there is no error.
for i=1:2
for j =1:2
AB(i,j) = A(i,j)^B(i,j);
end
end
AB =
-1 1
1 -1
I can also select a single power coefficient and get the correct values, such as
A.^B(1,2)
ans =
1 1
1 1
What's wrong with the matrix element-wise power? Why is it giving out imaginary numbers and NaN for essentially 0^0, which should equal 1. Thanks.
EDIT: More Information on Replicating the Error
I tried to figure out why others can't replicate the errors I'm getting. After much frustration, I restarted the computer (Windows 10, R2018a) and tried it from a fresh instance, just copying and pasting the code into the Command Window, I get no error. However, if I run it from a script (e.g., script.m with the exact same code), then I get the error, and once it's errored, it can't be undone. Did some system settings change once I run it from an M file? I hope this helps to pinpoint the problem.
>> A = [-1, 0; 0, -1];
B = [1, 0; 0, 1];
A.^B
ans =
-1 1
1 -1
>> script
ans =
-1.0000 + 0.0000i NaN + 0.0000i
NaN + 0.0000i -1.0000 + 0.0000i
>> A = [-1, 0; 0, -1];
B = [1, 0; 0, 1];
A.^B
ans =
-1.0000 + 0.0000i NaN + 0.0000i
NaN + 0.0000i -1.0000 + 0.0000i
10 commentaires
Réponse acceptée
James Tursa
le 24 Jan 2020
Looks like the problem calculation is being done in the background as exp(B.*log(A)), but I don't know why it does this sometimes and not other times.
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