# How to use randperm with minimum spacing between random numbers

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Gordon Ariho on 30 Aug 2019
Edited: Bruno Luong on 30 Aug 2019
Hi
I would like to use randperm but be able to specify the minimum separation between the random numbers generated. Please advise.
p = randperm(n,k) returns a row vector containing k unique integers selected randomly from 1 to n inclusive.
I would like to have the k intergers to have atleast a separation of say b when sorted.
Thanks
Gordon

#### 1 Comment

Guillaume on 30 Aug 2019
What sort of values are n, k and b? If n>>k and n>>b then you could just retry randperm until you've got a set that satisfies your condition.

Bruno Luong on 30 Aug 2019
Edited: Bruno Luong on 30 Aug 2019
n=20;
k=3;
b=7;
[as,is]=sort(randperm(n-(k-1)*(b-1),k)); % if it throws an error then b/k/n are not compatible
a = as + (0:k-1)*(b-1);
a = a(is)

James Tursa on 30 Aug 2019
Maybe something like this will suffice for your needs?
p = b * randperm(floor(n/b),k)
If n/b isn't an integer value, then there be some "missing" higher numbers. (Or could adjust this so the "missing" numbers are the lower numbers or are perhaps randomly scattered throughout the range).