Hey, I'm new to MATLAB and was stuck on a problem which requires me to calculate the expectation value of a poisson distribution by summing the probability mass function *k ie P = k*lambda^k*exp(-lambda)/factorial(k) for k= 1 to infinity. I thought of using "for k1:1000 P =... " but then had no idea how to sum the individual results. Any help much appreciated. =) edit: I think I've sorted it out now by having a sum term initialised before and included into the loop. However, Im finding that if I increase k to above a value of 400 or so, both the answer for the poisson process and the sum become NaN. Surely, the probability should just reach 0 and the expectation value just 5. Is there any way to avoid this?