How to create a matrix from multiples of submatrice?
2 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Timon Viola
am 11 Jun. 2020
Bearbeitet: madhan ravi
am 11 Jun. 2020
I would like to find a smarter way of building a larger matrix from vectors. The following code works fine:
rv = [1 2 3 4];
alpha =[0.0140;
0.0100;
0.0100;
0.0100];
c = [];
for i = 1:4
c = [c; diag(alpha).*rv(i)];
end
>> c =
0.0140 0 0 0
0 0.0100 0 0
0 0 0.0100 0
0 0 0 0.0100
0.0280 0 0 0
0 0.0200 0 0
0 0 0.0200 0
0 0 0 0.0200
0.0420 0 0 0
0 0.0300 0 0
0 0 0.0300 0
0 0 0 0.0300
0.0560 0 0 0
0 0.0400 0 0
0 0 0.0400 0
0 0 0 0.0400
Essentially I build a submatrix from a vector. Then I multiple the diagonal submatrix with each element of a vector. Then I concatenate these vertically.
Is there a computationally more efficient way of doing this?
Thanks!
0 Kommentare
Akzeptierte Antwort
madhan ravi
am 11 Jun. 2020
Bearbeitet: madhan ravi
am 11 Jun. 2020
Z = reshape(rv,1,1,[]) .* diag(Alpha);
Wanted = reshape(Z,numel(rv),[]).'
2 Kommentare
Michael Soskind
am 11 Jun. 2020
Even more confusing but with no tansposes and in one line:
repmat(diag(alpha),4,1).*reshape(repmat(rv, 4,4),[],4)
madhan ravi
am 11 Jun. 2020
Bearbeitet: madhan ravi
am 11 Jun. 2020
" and in one line"
Wanted = reshape(reshape(rv,1,1,[]) .* ...
diag(Alpha),numel(rv),[]).'
"Even more confusing"
Why?
N = 1e6;
tic
for k = 1:N
Z = reshape(rv,1,1,[]) .* diag(Alpha);
Wanted = reshape(Z,numel(rv),[]).';
end
% Elapsed time is 4.847994 seconds.
toc
tic
for k = 1:N
repmat(diag(alpha),4,1) .* reshape(repmat(rv, 4,4),[],4);
end
toc
% Elapsed time is 5.865444 seconds.
Weitere Antworten (0)
Siehe auch
Kategorien
Mehr zu Creating and Concatenating Matrices finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!