Computes cumulative distribution function (cdf) of the gamma shape mixture (GSM) model. The general form for the cdf of the GSM model is given by
$$F(x,{\Theta}) = \sum_{j=1}^{K}\omega_j F(x,j,\beta),$$
where
$$F(x,j,\beta) = \int_{0}^{x} \frac{\beta^j}{\Gamma(j)} y^{j-1} \exp\bigl( -\beta y\bigr) dy,$$
in which \(\Theta=(\omega_1,\dots,\omega_K, \beta)^T\) is the parameter vector and known constant \(K\) is the number of components. The vector of mixing parameters is given by \(\omega=(\omega_1,\dots,\omega_K)^T\) where \(\omega_j\)s sum to one, i.e., \(\sum_{j=1}^{K}\omega_j=1\). Here \(\beta\) is the rate parameter that is equal for all components.