# Find the indices of the imaginary element of the matrix

2 views (last 30 days)
Hassan Alkomy on 8 Jun 2021
Answered: Hassan Alkomy on 8 Jun 2021
Suppose I have a Matrix like this:
A=[1 2 3;
4+i 5 6-i;
7 8+i 9]
Now, I want to know if there is a way to find the indecies of the imaginary elements (by this I mean the complex numbers which have imaginary part). I am looking for an answer like that:
A(2,1)
A(2,3)
A(3,2)
or any other form the conveys the indecies information of the imaginary elements.
Thank you so much.

David Hill on 8 Jun 2021
Lidx=find(imag(A)~=0);
##### 2 CommentsShowHide 1 older comment
Hassan Alkomy on 8 Jun 2021
Thank you so much.

Joseph Cheng on 8 Jun 2021
you can do a comparison to the real(A) like
A=[1 2 3;
4+i 5 6-i;
7 8+i 9]
A =
1.0000 + 0.0000i 2.0000 + 0.0000i 3.0000 + 0.0000i 4.0000 + 1.0000i 5.0000 + 0.0000i 6.0000 - 1.0000i 7.0000 + 0.0000i 8.0000 + 1.0000i 9.0000 + 0.0000i
[row col]=find(A~=real(A))
row = 3×1
2 3 2
col = 3×1
1 2 3
then with find you can get the row and column index values of the as real(A)~=A
Hassan Alkomy on 8 Jun 2021
Thank you so much.

Scott MacKenzie on 8 Jun 2021
% test matrix
A=[1 2 3;
4+i 5 6-i;
7 8+i 9]
% identify imaginary elements in A (+1 or -1)
B = imag(A)
% generate column vector of indices of imaginary elements in A
find(B~=0)
Output:
A =
1 + 0i 2 + 0i 3 + 0i
4 + 1i 5 + 0i 6 - 1i
7 + 0i 8 + 1i 9 + 0i
B =
0 0 0
1 0 -1
0 1 0
ans =
2
6
8
Hassan Alkomy on 8 Jun 2021
Thank you so much.

Hassan Alkomy on 8 Jun 2021
Actually, the three solutions by David, Joseph and Scott give what i want. I chose David's answer because it is a one-line answer, but the rest of the solutions gives the same result.
Thank you all.

R2019a

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