Is there a better way to perform a moving window of operations without using a for loop?

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razorfin 2017-9-6

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评论： John Chilleri 2017-9-10

采纳的回答： John Chilleri

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Say I have a matrix:

x=1:100;

And I want to create a new matrix y that has the following output:

[sqrt(1^2+4^2), sqrt(2^2+5^2), sqrt(3^2+6^2), ... etc.]

Note that each term in the output is y[index]=sqrt(x[index]^2+x[index+3]^2).

I could accomplish this with a for loop, but if matrix x is really large this is inefficient. Is there a more efficient way?

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Answer 1

John Chilleri 2017-9-6

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编辑：John Chilleri 2017-9-6

在 MATLAB Online 中打开

Hello,

You can figure out a way to use vector notation,

x = 1:100;
y = sqrt(x(1:end-3).^2+x(4:end).^2);

I ran this vs the for loop version you have above, and this performed twice as fast when x = 1:1000000 and three times faster when x = 1:100000000. Although it didn't take long for either, I'd be more concerned for memory than speed - but that's only regarding this problem.

Hope this helps!