In order to test my program I need to calculate 95% confidence intervals (preferably even CDF) for a distribution of a renewal process with hypoexponentially distributed holding times: $X = X_{\lambda_1} + X_{\lambda_2}$, where $X_{\lambda_i}$ is an exponential distribution with ratio $\lambda_i$.
If the holding times were distributed exponentially I would use available implementation of Poisson distribution. However, with hypoexponential holding times I have no idea:
- whether there is a particular name for such distribution,
- how can I calculate such CDF (excluding Monte Carlo simulations).
I would appreciate any help.