The function evaluates the cdf of the univariate \(p\)-generalized normal distribution according to the density $$f(x,p,mean,\sigma)=(\sigma_p/ \sigma) \, C_p \, \exp \left( - \left( \frac{\sigma_p}{\sigma } \right)^p \frac{\left| x-mean \right|^p}{p} \right) ,$$ where \(C_p=p^{1-1/p}/2/\Gamma(1/p)\) and \(\sigma_p^2=p^{2/p} \, \Gamma(3/p)/\Gamma(1/p) \).