Calculates the beta binomial infection history prior for each individual, taking into account the number of years they could be infected.
infection_history_prior(pars, infection_history, age_mask)the named parameter vector with infection_model_prior_shape1 and infection_model_prior_shape2 corresponding to the beta binomial distribution
the infection history matrix
the age mask, giving the first index of the infection_history matrix that each individual can be exposed to. One entry per individual
the log prior contribution for each individual