Save loop data to a matrix

Question

Harshil Patel 2016-3-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/270963-save-loop-data-to-a-matrix

评论： Muhamad Bunaiya 2018-4-5

Hello,

It would be a great help if someone could suggest a way to save data from the loop in a matrix. I am using the following code.

p = [1,2,3;4,5,6];
for i = 1:3
    x = p(1,i);
    y = p(2,i);
    u1 = [x*y x/y 2*x];
    u2 = [y/x x*y y/2];
end

For each iteration of the loop, the values of u1 and u2 will change. Now, I want to store this u1 and u2 values in matrix U, such that at the end of the loop U will be:

U =
 u1     %from i = 1
 u2     %from i = 1
 u1     %from i = 2
 u2     %from i = 2
 u1     %from i = 3
 u2     %from i = 3

I have searched through numerous threads on similar topics but haven't found a satisfactory answer. Could someone please help me with this.

Thanking You,

Harshil

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Muhamad Bunaiya 2018-4-5

xt=[1 2 3 4 5 6 7 8 9 10 11] for m=1:25

Output supposely xt1 = [1 2 3 4 5 6 7 8 9 10 11] xt2 =[1 2 3 4 5 6 7 8 9 10 11] . . . . . . . xt25 =[1 2 3 4 5 6 7 8 9 10 11] What should i do to get this output

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Answer 1

Guillaume 2016-3-2

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在 MATLAB Online 中打开

To do exactly what you asked:

p = [1,2,3;4,5,6];
U = zeros(size(p, 2)*2, 3);
for i = 1:size(p, 2)  %don't use hardcoded constants when you can just query the size
    x = p(1,i);
    y = p(2,i);
    U(2*i-1, :) = [x*y x/y 2*x];
    U(2*i, :) = [y/x x*y y/2];
end

However, I don't think interleaving your u1 and u2 is a good idea. It makes it more difficult to index. Instead, I would put u1 and u2 in the same row:

p = [1,2,3;4,5,6];
U = zeros(size(p, 2), 6);
for i = 1:size(p, 2)  %don't use hardcoded constants when you can just query the size
    x = p(1,i);
    y = p(2,i);
    U(i, 1:3) = [x*y x/y 2*x];
    U(i, 4:6) = [y/x x*y y/2];
end