Its difficult to understand your question, but if you would elaborate it would be great. Although, i would provide solution as per what i have interpreted.
1. It seems you want to store the values at different indexes, rather than in succession. Or 2. It seems you want to change the steps of progression.
In the above cases, solutions could be as follows... 1. define a dummy variable, say pos (as in "position") and at the end of every loop increment as per your requirement. Or 2. while defining the for loop, define the step as: "for i=start:stepsize:end"
In case i haven't interpreted the question properly, i would like you to elaborate it as per the requirement.
Hope it helps.