For loop: access values in between steps

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Simon Allosserie 2021-1-21

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https://ww2.mathworks.cn/matlabcentral/answers/722818-for-loop-access-values-in-between-steps

评论： Yvan Lengwiler 2021-1-21

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I have a for-loop where first only certain rows of a matrix are dealt with:

for i = 1:3:100 %3 is an example step size, the step size is a variable in the program
    %do something with rows 1, 4, 7, 10, 13, 16 ...
end

After this, the remaining rows, i.e. rows 2,3, 5,6, 8,9, ... need to be filled up using the data in the rows calculated above. I don't see which would then be the most optimal method to define this new for loop. Possibly, for loops aren't even the best way to approach this? Thanks for your input!

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Mathieu NOE 2021-1-21

hello Simon

if your computations can be vectorize there is no need to do for loops here

now, if you have to do more complicated stuff like doing ode solving for example , there is no other way than doing it with a for loop

it all depends on what the computation is about

Simon Allosserie 2021-1-21

Hey Mathieu

The computations cannot be vectorized, I fear.

There is a small "scanning matrix" that hovers over the big matrix in which I adapt the rows depending on the interactivity between the data in the small and the large matrix, and this for each cell in the selected rows.

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Yvan Lengwiler 2021-1-21

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https://ww2.mathworks.cn/matlabcentral/answers/722818-for-loop-access-values-in-between-steps#answer_602888

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for i = 1:3:100
    %do something with rows 1, 4, 7, 10, ...
end
for i = 2:3:100
    %do something with rows 2, 5, 9, 11, ...
end
for i = 3:3:100
    %do something with rows 3, 6, 10, 12, ...
end