Writing a code for taking averaging at a point

I have vector of 100x1. Say 1-100. I want to take average at a particular point say 40. I want the average to be done in such a way that it will take 20 values on top and below 40 and add 40 itself making a total of 41 of sample. How can I write a code for this on matlab?

Answer 1

[per isakson]

Run

    vec = transpose(1:100);
    ix  = 40;
    rng = 20;
    avg = mean( vec( ix-rng : ix+rng ) );

and

    >> avg
    avg =
        40