get_phi_yt
computes the intercept \(\phi_{y,t}=\sum_{m=1}^M \alpha_{mt} \phi_{m}\) parameter
value for a single time period based on the regime intercepts and transition weights.
get_phi_yt(all_phi0, alpha_mt)
Returns the \((d \times 1)\) vector of the intercept parameter values for the time period \(t\).
a \((d \times M)\) matrix such that the \(m\)th column contains the intercept parameters of the \(m\)th regime.
an \((M \times 1)\) vector containing the time period \(t\) transition weights.
This is used in simulation of the counterfactual scenarios.