How to Find Index of Repeated Elements in a Vector?

I have a vector, for example:

x = [7, 22, 16, 20, 22, 3, 6, 22, 5]

I would like to first look the nth element of the vector, and then check the other indices to see if this value is repeated.

For example:

x(5) = 22. 

How would I find the other indices of x which are also 22? In this example, I would expect a return of x(2) and x(8).

Answer 1

[Jan]

x = [7, 22, 16, 20, 22, 3, 6, 22, 5]
index = 5;

a = x(5)
index = find(x == a)

% Or:
[UniqX, iX, iUniqX] = unique(x)

[Stuart Shanks]

Works like a charm, thanks!