Element-wise power resulting in imaginary values and NAN
3 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
MathN00b
am 23 Jan. 2020
Kommentiert: Walter Roberson
am 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 Kommentare
Akzeptierte Antwort
James Tursa
am 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.
2 Kommentare
Weitere Antworten (0)
Siehe auch
Kategorien
Mehr zu Data Extraction finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!