How to do a layered matrix--vector multiplication without a for loop?
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Anne Davenport
am 26 Jan. 2024
Verschoben: Bruno Luong
am 29 Jan. 2024
I would like to multiply a 3-D matrix of NNN transformations by a 2-D matrix of NNN vectors without the for loop below:
% RR is an (NNN x 3) array of vectors.
% TT is a 3-D array of NNN (3 x 3) matrices.
for iii = 1:1:NNN
TRR(iii,:) = TT(:,:,iii) * RR(iii, 3);
end
The array of transformed vectors is an (NNN x 3) matrix.
I have tried pagemtimes() with no luck. Any help would be much appreciated.
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Bruno Luong
am 26 Jan. 2024
Bearbeitet: Bruno Luong
am 26 Jan. 2024
NNN = 10;
RR = rand(NNN, 3);
TT = rand(3,3,NNN);
for iii = 1:1:NNN
TRR(iii,:) = TT(:,:,iii) * RR(iii, :).'; % Bug fix
end
TRR1 = permute(pagemtimes(TT, reshape(RR.', 3, 1, [])), [3 1 2]);
norm(TRR-TRR1, 'inf')
% EDIT:
TRR
TRR1
4 Kommentare
Dyuman Joshi
am 27 Jan. 2024
@Anne Davenport, the elements do match, see the edit above.
You can directly check like this as well -
NNN = 10;
RR = rand(NNN, 3);
TT = rand(3,3,NNN);
for iii = 1:1:NNN
TRR(iii,:) = TT(:,:,iii) * RR(iii, :).'; % Bug fix
end
TRR1 = permute(pagemtimes(TT, reshape(RR.', 3, 1, [])), [3 1 2]);
all(TRR-TRR1==0, 'all')
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