Precompute shape of posterior distribution for epsilon
get_shape_epsilon(incid, lambda, priors, t_min = 2L, t_max = nrow(incid))a multidimensional array containing values of the (local) incidence for each time step (1st dimension), location (2nd dimension) and pathogen/strain/variant (3rd dimension)
a multidimensional array containing values of the overall infectivity for each time step (1st dimension), location (2nd dimension) and pathogen/strain/variant (3rd dimension). The overall infectivity for a given location and pathogen/strain/variant represents the sum of the incidence for that location and that pathogen/strain/variant at all previous time steps, weighted by the current infectivity of those past incident cases. It can be calculated from the incidence `incid` and the distribution of the serial interval using function `compute_lambda`)
a list of prior parameters (shape and scale of a gamma distribution) for epsilon and R; can be obtained from the function `default_priors`. The prior for R is assumed to be the same for all time steps and all locations
an integer >1 giving the minimum time step to consider in the estimation. Default value is 2 (as the estimation is conditional on observations at time step 1 and can therefore only start at time step 2).
an integer >`t_min` and <=`nrow(incid)` giving the maximum time step to consider in the estimation. Default value is `nrow(incid)`.
a value or vector of values of the shape of the posterior distribution of epsilon for each of the non reference variants
n_loc <- 4 # 4 locations
n_v <- 3 # 3 strains
T <- 100 # 100 time steps
priors <- default_priors()
# constant incidence 10 per day everywhere
incid <- array(10, dim = c(T, n_loc, n_v))
incid <- process_I_multivariant(incid)
# arbitrary serial interval, same for both variants
w_v <- c(0, 0.2, 0.5, 0.3)
si_distr <- cbind(w_v, w_v, w_v)
lambda <- compute_lambda(incid, si_distr)
get_shape_epsilon(incid$local, lambda, priors)
#> [1] 3961 3961