Extracting only real numbers from a vector containing both real and complex values
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Tanveer Ashiq
el 19 de Mzo. de 2021
Editada: Ahmadreza Torabi
el 15 de Dic. de 2021
Hi, I have a matrix that contains both real and complex elements in it. How can I transfer all the real elements (NOT the real parts of all elements) to another matrix?
For example:
My orginal matrix is A:
A = [ -0.4406 - 1.5696i , -0.4406 + 1.5696i, 1.8812 + 0.0000i]
Here we see that A has 3 elements, the first two of which are complex while the third element is real. How do I write code that extracts only the real element ie, the third element (1.8812)?
I do NOT want to extract the real parts of all three variables.
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Daniele Mascali
el 19 de Mzo. de 2021
Try this:
real(A(imag(A) == 0))
2 comentarios
Rik
el 19 de Mzo. de 2021
If you run into any issues with float rounding errors:
A = [ -0.4406 - 1.5696i , -0.4406 + 1.5696i, 1.8812 + 0.0000i];
A(4)= 1 + 1i*(sqrt(2)^2-2); % imaginary part should be 0 but isn't quite
B1=real(A(imag(A) == 0));
B2=real(A(abs(imag(A))<(10*eps)));
disp(A),disp(B1),disp(B2)
Mathieu NOE
el 19 de Mzo. de 2021
that's why I suggested to make a test with a given tolerance and not exact zero match with risks of wrong answer due to rounding errors
Más respuestas (2)
Mathieu NOE
el 19 de Mzo. de 2021
hello
see code below :
A = [ -0.4406 - 1.5696i , -0.4406 + 1.5696i, 1.8812 + 0.0000i];
tol = eps;
ind = find(abs(imag(A))<tol);
B = A(ind);
1 comentario
Ahmadreza Torabi
el 15 de Dic. de 2021
Editada: Ahmadreza Torabi
el 15 de Dic. de 2021
Hello
You can use something like this:
A = [1 2 7+i 3 8+i 4 9+i 5 6];
m = 1;
n = length(A);
for k = 1:n
if isreal(A(k))
B(m) = A(k);
m = m+1;
end
end
B
Then B is just include real numbers of A.
1 comentario
Rik
el 15 de Dic. de 2021
This will dynamically grow the array. It is better to create a logical vector of the same size as A where you mark wether it should be removed. Then you only need to modify the B once: when you create it.
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