# How to simplify the for loop for 3D matrix?

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Kalasagarreddi Kottakota am 11 Jan. 2023
Kommentiert: Bruno Luong am 11 Jan. 2023
I have the following code, where I am looking to eliminate only the outer for-loop (k) and include 'k' inside the inner loop. Here, I perform inverse considering each calculation point (k=1:NFocP) in a loop, but would like to some how eliminate outer loop and perform the inverse for all points at one instance. And the other concern is that I don't want to disturb the mldivide (\) function. Is there any way to solve this issue?
clear all;
Foc = size(s1,3); % no of calculation points
Nt = size(s1,2); % length of signal
M = size(s1,1); % no of rsensors
for k=1:Foc
for p = 1:Nt
H = [s1(:,p,k) s2(:,p,k)];
tmp = H\ A(:,p);
Ainv1(k,p) = tmp(1);
Ainv2(k,p) = tmp(2);
end
end
##### 2 KommentareKeine anzeigenKeine ausblenden
Benjamin Thompson am 11 Jan. 2023
That would require calculating an inverse of a 3D matrix for H which is not possible. You may be able to use foreach to speed up the code by doing the outer loops in parallel.
Kalasagarreddi Kottakota am 11 Jan. 2023
Attached H and A1
The matrix H looks like 9 x 2 x 14 and matrix A1 is 9 x1. I need to perform inversion between every page of H with A1 using mldivide so that output looks like 2 x 1 x14 matrix. No loops. Is this possible?
clear all;
close all;

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### Akzeptierte Antwort

Bruno Luong am 11 Jan. 2023
Bearbeitet: Bruno Luong am 11 Jan. 2023
[m,n,p] = size(s1);
% s = [reshape(s1, [m,1,n,p]), reshape(s2, [m,1,n,p])];
% Ar = reshape(A,m,1,[]);
% C=pagemldivide(s,Ar);
% Ainv1=reshape(C(1,:,:),n,p).';
% Ainv2=reshape(C(2,:,:),n,p).';
s = reshape([s1;s2], [m,2,n,p]);
Ainv1 = zeros(p,n);
Ainv2 = zeros(p,n);
for i=1:n
C=pagemldivide(s(:,:,i,:),A(:,i));
Ainv1(:,i)=C(1,:);
Ainv2(:,i)=C(2,:);
end
##### 4 Kommentare2 ältere Kommentare anzeigen2 ältere Kommentare ausblenden
Kalasagarreddi Kottakota am 11 Jan. 2023
Bearbeitet: Kalasagarreddi Kottakota am 11 Jan. 2023
Ok, I see now. I have 2021. Is there any possibility to replace pagemldivide with any other alternate functions to do same task?
Bruno Luong am 11 Jan. 2023
You might try this that requires the FEX
https://fr.mathworks.com/matlabcentral/fileexchange/27762-small-size-linear-solver#functions_tab
[m,n,p] = size(s1);
s = reshape([s1;s2], [m,2,n,p]);
Ainv1 = zeros(p,n);
Ainv2 = zeros(p,n);
Ar = reshape(A,m,1,[]);
scs = pagemtimes(s,'ctranspose',s,'none');
scA = pagemtimes(s,'ctranspose',Ar,'none');
for i=1:n
scsi = reshape(scs(:,:,i,:),2,2,[]);
scAi = reshape(scA(:,:,i,:),2,1,[]);
C = inv2(scsi, scAi); % https://fr.mathworks.com/matlabcentral/fileexchange/27762-small-size-linear-solver#functions_tab
Ainv1(:,i)=C(1,:);
Ainv2(:,i)=C(2,:);
end

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