create Matlab function to preform a running average filter

hi there I am clueless on how to create Matlab function to preform a running average filter using the following data:

[1 9 10 11 12 13 14 15 14 13 12 11 10 9 1]

may someone help me please and thank you

[Yao Li]

I think it depends on the precision of the filter. Do you want to calculate the mean value of ervery 3 points, 5 points or 7 points, etc?

Answer 1

[Jan]

You can use filter to achieve this:

x = [1 9 10 11 12 13 14 15 14 13 12 11 10 9 1];
n = 3;  % Number of elements to be averaged
y = filter(ones(1, n) / n, 1, x);

But perhaps this does not satisfy your demands at the edges. You can do it manually also:

m = (n - 1) / 2;
len = size(x, 2);
y = x;
div = ones(size(x));
for k = 1:m
   k2 = 2*k;   % Slightly faster
   z  = zeros(1, k);
   y  = y + [z, x(1:len - k2) + x(1 + k2:len), z];
   div(k + 1:len - k) = div(k + 1:len - k) + 2;
end
y = y ./ div;

Here the first and last elements are not changed, while the 2nd and 2nd last are averaged using 3 elements for all n >= 3.

You will find much more approachs, when you search in the FileExchange. It is a good idea to check, if others have published a solution there, before you ask in the forum.

Answer 2

[Ma sa]

How can i creat an average filter of size(3*3)??