Forming a block diagonal matrix of one certain matrix?

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sn at
sn at am 14 Feb. 2017
Bearbeitet: Bruno Luong am 30 Jan. 2021
I have a matrix A which is m*n. I want to create a block diagonal matrix of size 100*100 whose diagonal elements are the matrix A.
[A,0,0,0
0,A,0,0
0,0,A,0
0,0,0,A
... ]
function, out = blkdiag(A,A,A,A,...) needs writing down the matrix so many times. Is there any other way to do this (not typing so many matrices as input arguments of blkdiag)?
  2 Kommentare
Teun Burgers
Teun Burgers am 18 Apr. 2018
how about
kron(eye(100),A)
or
kron(eye(100),sparse(A))
Rik
Rik am 30 Jan. 2021
Comment posted as flag by @Anubhav Halder:
Worked perfectly for me. Thanks.

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Akzeptierte Antwort

Star Strider
Star Strider am 14 Feb. 2017
Cell arrays create comma-separated lists, which are exactly what the blkdiag function wants as its arguments.
See if this does what you want:
A = [1 2; 3 4]; % Original Matrix (Created)
N = 3; % Number Of Times To Repeat
Ar = repmat(A, 1, N); % Repeat Matrix
Ac = mat2cell(Ar, size(A,1), repmat(size(A,2),1,N)); % Create Cell Array Of Orignal Repeated Matrix
Out = blkdiag(Ac{:}) % Desired Result
Out =
1 2 0 0 0 0
3 4 0 0 0 0
0 0 1 2 0 0
0 0 3 4 0 0
0 0 0 0 1 2
0 0 0 0 3 4
  3 Kommentare
Star Strider
Star Strider am 24 Okt. 2019
My pleasure!
I appreciate your compliment!
Bruno Luong
Bruno Luong am 30 Jan. 2021
Bearbeitet: Bruno Luong am 30 Jan. 2021
The MAT2CELL step can be removed
A = [1 2; 3 4];
Ac = repmat({A}, 1, 3);
Out = blkdiag(Ac{:})

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Weitere Antworten (2)

Teun Burgers
Teun Burgers am 19 Apr. 2018

how about:

kron(eye(100),A)

or

kron(eye(100),sparse(A))

Honglei Chen
Honglei Chen am 14 Feb. 2017
eval(sprintf('Out = blkdiag(A%s);',repmat(',A',1,99)))
HTH
  1 Kommentar
Stephen23
Stephen23 am 18 Apr. 2018
Bearbeitet: Stephen23 am 18 Apr. 2018
The MATLAB documentation for eval recommends that "Whenever possible, do not include output arguments within the input to the eval function, such as eval(['output = ',expression]). The preferred syntax,"
output = eval(expression)
"allows the MATLAB parser to perform stricter checks on your code, preventing untrapped errors and other unexpected behavior." Because the variable Out does not change this could easily have been achieved in this solution, and thus would follow the advice given in the MATLAB help.
Note that Star Strider's solution avoids all of these problems by simply avoiding eval entirely:

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