How to create a large matrix using another matrix
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Petros Tsitouras
le 30 Mai 2020
Commenté : Petros Tsitouras
le 1 Juin 2020
Hello everyone, I want to make a large matrix (10^7 x 10^7) but it needs to have the following matrix being repeated around its main diagonal.
a=4;
A=[1 0 a+1 0;
a+2 2 0 a+1;
0 a+2 3 0;
0 0 a+2 4];
As you can see it is a main diagonal with 1:10^7 and 1 row lower repeating the number 6 and 2 rows higher repeating the number 5.
Everything I have tried turns out to be huge in terms of memory and unable to be performed like that. I suppose the trick is by somehow making use of a sparse matrix, but I cannot get it to work properly.
Thanks a lot in advance!
8 commentaires
Walter Roberson
le 1 Juin 2020
Your original request shows the a+2 below the diagonal, so anything that ends up with the 6 above the diagonal is a wrong approach ;-)
The approach I used of constructing columns instead of rows has the advantage of not needing to transpose Acom, and so is more efficient.
Réponse acceptée
Walter Roberson
le 30 Mai 2020
Modifié(e) : Walter Roberson
le 1 Juin 2020
4 commentaires
Walter Roberson
le 30 Mai 2020
a=4;
N=1E7;
Adiag=(1:N).';
A1=ones(N,1)*(a+2);
A2=ones(N,1)*(a+1);
Acom=[A2, Adiag, zeros(N,1), A1];
B=spdiags(Acom,-1:2,N,N);
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