Eliminate a for loop to increase speed

1 Ansicht (letzte 30 Tage)
Howard Wilton
Howard Wilton am 23 Nov. 2022
Kommentiert: Howard Wilton am 25 Nov. 2022
I have a code snippet below which uses a for loop that I am trying to eliminate as I need to scale up to larger values of N and L.
clc; clearvars;
N = 2; L = 2; T = 1;
a = [1 1i; -1i -1];
nplq = int8(de2bi((0:2^(N*L)-1),'left-msb')); % [0 0 0 0; 0 0 0 1; 0 0 1 0; ... ; 1 1 1 1]
a_nl = zeros(2^(N*L),1);
for i = 1:2^(N*L)
a_nl(i) = a(nplq(i,1)+1,nplq(i,3)+1);
end
% wish i could do something like a_nl = a(nplq(:,1),nplq(:,3))
Any suggestions would be appreciated.

Akzeptierte Antwort

Jan
Jan am 23 Nov. 2022
Bearbeitet: Jan am 23 Nov. 2022
N = 2; L = 2; T = 1;
a = [1 1i; -1i -1];
nplq = int8(de2bi((0:2^(N*L)-1),'left-msb')); % [0 0 0 0; 0 0 0 1; 0 0 1 0; ... ; 1 1 1 1]
a_nl = zeros(2^(N*L),1);
for i = 1:2^(N*L)
a_nl(i) = a(nplq(i,1) + 1, nplq(i,3) + 1);
end
% Without a loop:
a_nl2 = a(sub2ind(size(a), nplq(:,1) + 1, nplq(:,3) + 1));
isequal(a_nl, a_nl2) % Same result?
ans = logical
1
Do you really need the complete nplq matrix or are the 2 columns enough?
N = 2; L = 2;
M = 2^(N*L - 1)
v = uint8(1:2).';
nplq1 = repelem(v, M, 1);
c = 3 - 1; % 3rd column
nplq3 = repmat(repelem(v, M / 2^c, 1), 2^c, 1);
  3 Kommentare
Jan
Jan am 24 Nov. 2022
The creation of nplq can be expensive, if it exhausts the free memory: It is created as double at first, which needs 8 times the RAM of the needed UINT8 array. If this is a problem, you can try the C-mex function: FEX: VChoseKRO:
VChooseKRO_M(uint8([0,1]), N*L)
Howard Wilton
Howard Wilton am 25 Nov. 2022
Thank you very much!

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (0)

Produkte


Version

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by