how to use circshift in matlab

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?

[Image Analyst]

Please give an example. Just saying "put it M-2" is not descriptive enough. circshift works on the whole array, it does not use different shifts on an element by element basis.

[ss]

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]

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

Answer 1

[Matt J]

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

 mod(i,M)

[Roger Stafford]

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