how to speed up this nestled for loop

Question

Jeroen 2012-2-17

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关闭： MATLAB Answer Bot 2021-8-20

Hi everybody,

I need to make this code faster:

for i=1:n1*n2*n3;
    x1 = M(i,1);
    y1 = M(i,2);
    ex1 = M(i,4);
    ey1 = M(i,5);
    ez1 = M(i,6);
    if x1 <= 70 && x1 >= -70 && y1 <= 70 && y1 >= -70;
        ex2 (i) = 0;
        ey2 (i) = 0;
        ez2 (i) = 0;
    else
        ex2 (i) = ex1;
        ey2 (i) = ey1;
        ez2 (i) = ez1;
    end
end

What is the best way to do that?

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Answer 1

Andrei Bobrov 2012-2-17

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在 MATLAB Online 中打开

try this is code

exyz = zeros(size(M(:,4:6)));
t = all(M(:,1:2) >= -70 & M(:,1:2) <= 70,2);
exyz(t,:) = M(t,4:6);

ADD

so?

exyz2 = zeros(size(M(:,4:6)).*[1 2]);
t = all(M(:,1:2) >= 70 & M(:,1:2) <= 70,2);
exyz2(:,1:3) = M(:,4:6);
exyz2(t,4:6) = M(t,4:6);

ADD2

out = M;
t = all(M(:,1:2) >= 70 & M(:,1:2) <= 70,2);
out(t,4:6) = out(t,4:6);

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Answer 2

Jeroen 2012-2-17

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Thank Andrei Bobrov for your fast answer. But this yields a 235238 by 3 matrix and it needs to be a 235238 by 6 matrix. Anyway with your tips I can probably do something

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Andrei Bobrov 2012-2-17

in our case:

exyz2 == [ex2 ey2 ez2]

Answer 3

Jeroen 2012-2-17

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https://ww2.mathworks.cn/matlabcentral/answers/29407-how-to-speed-up-this-nestled-for-loop#answer_37776

Okay thank you for your respons! But this is not what i want. i have matrix M. That matrix has 6 rows and 235238 columns. Now if there is a value in that matrix that is below -70 or above 70 that element has to be zero.

The matrix that i create looks like: M = [M(:,1),M(:,2),M(:,3),ex2,ey2,ez2]; With ex2,ey2,ez2 the values that i have in the for loop.

Sorry for the late respons. I did not got a mail.