how to use circshift in matlab

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ss 2012-12-21

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I have a array of indeces, so they must be positive, but some of them are negative, for instance for a array of m elements, I want to say if i=-1 put i=M-1, and if i=-2 put it M-2, how can I use circshift?

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ss 2012-12-21

I mean my data are periodic, yes you are right, my problem is exactly what you say. I find indeces that their number is M-an M-dimensional array-but I want to say if one of this numbers is out of 0 to M-1, select it such as it be between 0 to M-1, for instance if it is -1 select it as M-1, I don't want to use if loop, is there any method?

Image Analyst 2012-12-21

I think Matt is right - you want mod(), not circshift().

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Matt J 2012-12-21

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编辑：Matt J 2012-12-21

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What you're trying to do does not seem to require CIRCSHIFT at all, but merely

mod(i,M)

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Roger Stafford 2012-12-22

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If positive integers are desired which must always fall in the range 1<=k<=M, then a modification of the 'mod' function would seem to be called for. To "add" p to k, do this:

k_plus_p = mod(k+p-1,M)+1

This gives the alteration to an index k of an element of an array which occurs with a circular shift of amount p.

Roger Stafford

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