Converting a 2d array into a 3d array

12 Ansichten (letzte 30 Tage)
Vinay Killamsetty am 28 Nov. 2021
Beantwortet: Turlough Hughes am 28 Nov. 2021
Hi,
I am having a 2d array with size mxn
I want to convert each column into a seperate 2d diagonal matrix--- a total of 'n' diagonal matrices of size mxm
Then combining all the 2d diagonal matrices as a single 3d matrix.---size mxmxn
I tried to do this with employing a for-loop but it is taking lot of time
Can this be done without using a loop and at a faster speed?
2 KommentareKeine anzeigenKeine ausblenden
Turlough Hughes am 28 Nov. 2021
Can you give an example of the code you have implemented?
Vinay Killamsetty am 28 Nov. 2021
Bearbeitet: Vinay Killamsetty am 28 Nov. 2021
size of Z_int is mxn
Z = nan(m,m,n)
for i = 1 : size( Z_int , 2)
Z( : , : , i ) = diag( (Z_int( :, i ) ) ;
end

Melden Sie sich an, um zu kommentieren.

Antworten (2)

Chunru am 28 Nov. 2021
"it is taking lot of time" for what size of array?
m=200; n=100;
Z_int = rand(m, n);
Z = nan(m,m,n);
tic
for i = 1 : size( Z_int , 2)
Z( : , : , i ) = diag( Z_int( :, i ) );
end
toc
Elapsed time is 0.009776 seconds.
0 Kommentare-2 ältere Kommentare anzeigen-2 ältere Kommentare ausblenden

Melden Sie sich an, um zu kommentieren.

Turlough Hughes am 28 Nov. 2021
You could write a linear index for the diagonal elements as follows:
[m,n] = size(Z_int)
Z = zeros(m,m,n);
idx = repmat((1:m+1:m^2).',1,n) + m^2*(0:n-1);
Z(idx(:)) = Z_int(:)
This is 2-4x faster for m >= 400 on my computer (n=500), however, on the matlab servers its a slightly slower. Whether it's faster or not for you will depend on your hardware, the size of your arrays and probably the version of matlab that you're using too.
0 Kommentare-2 ältere Kommentare anzeigen-2 ältere Kommentare ausblenden

Melden Sie sich an, um zu kommentieren.

Kategorien

Mehr zu Linear Algebra finden Sie in Help Center und File Exchange

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by