how do i store for loop values?

Question

row row 2021-8-29

0
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https://ww2.mathworks.cn/matlabcentral/answers/1442909-how-do-i-store-for-loop-values

评论： row row 2021-8-29

采纳的回答： Turlough Hughes

i have 3x920 double that call A

for k=1:length(A)-1 %% same as 1:919

Ax = A(2, k+1) - A(2,k)

end

Why is there only one value in the workspace?

i want something that 1x919 double

ex) Ax | 1x919

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Answer 1

Turlough Hughes 2021-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/1442909-how-do-i-store-for-loop-values#answer_776634

编辑：Turlough Hughes 2021-8-29

在 MATLAB Online 中打开

There's only one value because your code is working as follows:

for ii = 1:3
    A = ii + 1
end
A = 2
A = 3
A = 4

Matlab is not told where to store the data inside A, so A(1) just gets changed each time the loop iterates. You need to use the loop variable, ii, to indicate the index position in A where you would like to store data for the current iteration.

Let's try this again:

for ii = 1:3
    A(ii) = ii + 1
end
A = 2
A = 1×2
     2     3
A = 1×3
     2     3     4

We can do better though; it's important to preallocate the space to your variable when it's possible to do so:

A = zeros(1,3)
A = 1×3
     0     0     0
for ii = 1:3
    A(ii) = ii + 1
end
A = 1×3
     2     0     0
A = 1×3
     2     3     0
A = 1×3
     2     3     4