how to velocize it (vectorizing)

Question

aldo 2023-8-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2010552-how-to-velocize-it-vectorizing

编辑： Bruno Luong 2023-8-20

a=magic(10)
b=[4;5;9;2;3;4;2;7;4;9]  %width(a) element
x=ones(size(a));
for i=1:numel(b)
    x(1:max(b(i)-1,1),i)=0
end

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Answer 1

Bruno Luong 2023-8-20

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2010552-how-to-velocize-it-vectorizing#answer_1289947

编辑：Bruno Luong 2023-8-20

在 MATLAB Online 中打开

I don't know why a is matter beside that the first dimension is 10

a=magic(10);
b=[4;5;9;2;3;4;2;7;4;9];  %width(a) element
h = size(a,1);
x = double(ndgrid(1:h,b)>=b(:)')
x = 10×10
     0     0     0     0     0     0     0     0     0     0
     0     0     0     1     0     0     1     0     0     0
     0     0     0     1     1     0     1     0     0     0
     1     0     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     1     1     0
     1     1     0     1     1     1     1     1     1     0
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1

;

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Bruno Luong 2023-8-20

编辑：Bruno Luong 2023-8-20

在 MATLAB Online 中打开

" with max(b)<h is equal.. with max(b)>=h it is different"

because in that case your code grows x beyond the initial dimension of height h. Your final x will have more than h rows. Do you really want to do that?

h=7
h = 7
b=[4;5;9;2;3;4;2;7;4;9];
x=ones(h,numel(b));
for i=1:numel(b)
    x(1:max(b(i)-1,1),i)=0;
end
x
x = 8×10
     0     0     0     0     0     0     0     0     0     0
     0     0     0     1     0     0     1     0     0     0
     0     0     0     1     1     0     1     0     0     0
     1     0     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     1     1     0
     0     0     0     0     0     0     0     0     0     0
x1 = double(ndgrid(1:h,b)>=b(:)')
x1 = 7×10
     0     0     0     0     0     0     0     0     0     0
     0     0     0     1     0     0     1     0     0     0
     0     0     0     1     1     0     1     0     0     0
     1     0     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     0     1     0
     1     1     0     1     1     1     1     1     1     0
isequal(x(1:h,:), x1)
ans = logical
   1

As for speed I could possibly speed up, but who tells you that vectorized code must be faster?

aldo 2023-8-20

编辑：aldo 2023-8-20

"Yes for-loop is faster on onlive server (on my compter I get the opposite)." i don't use online server but my pc "Processore AMD Ryzen 9 5950X 16-Core Processor, 3401 Mhz, 16 core, 32 processori logici"

I think is better to use loop in my pc because it work with parallel processor

I've noticed dramatic improvements when it comes to vectorizing code where there is a loop inside another

thanks for taking the time