Simulink user defined block

I wanted to calculate the average of a particular array recursively, I am using this code shown below and I am using the user defined function on simulink to do this. I am getting the out of bounds error while i run the simulation, and when i debug, the averaging formula shown below is the problem. What could the reason be, although i feel like its a simple mistake that i am making

function poutavg = fcn(pout)

tstop=2*10^-3;
fsamp=4000000;

for i=2:tstop*fsamp

      poutavg =((i-1)/i)*mean(pout(1,i-1))+ (pout(1,i))/i;

      i=i+1;

end

[K E]

When I run this in Matlab it works fine, as long as length(pout) >= length(2:tstop*fsamp). So, check that the dimensions of pout are what you would expect.