Symmetrise a contact matrix

Makes a contact matrix symmetric so that \(c_{ij} N_i = c_{ji} N_j\), where \(c_{ij}\) is the (i, j) entry and \(N_i\) is the population of age group i. This is done by replacing each pair with half their sum, weighted by population size.

Usage

symmetrise(x, survey_pop, symmetric_norm_threshold = 2, ...)

Arguments

x

a list as returned by compute_matrix(), with elements matrix and participants

survey_pop

a data frame with columns lower.age.limit and population (e.g. from wpp_age())

symmetric_norm_threshold

threshold for the normalisation factor before issuing a warning (default 2)

...

passed to pop_age() for interpolation

Value

x with $matrix replaced by the symmetrised version

Examples

data(polymod)
pop <- wpp_age("United Kingdom", 2005)
polymod |>
  (\(s) s[country == "United Kingdom"])() |>
  assign_age_groups(age_limits = c(0, 5, 15)) |>
  compute_matrix() |>
  symmetrise(survey_pop = pop)
#> $matrix
#>          contact.age.group
#> age.group     [0,5)   [5,15)      15+
#>    [0,5)  1.9157895 1.281846 5.558271
#>    [5,15) 0.5994315 7.946078 7.428739
#>    15+    0.3882175 1.109550 9.594101
#> 
#> $participants
#>    age.group participants proportion
#>       <char>        <int>      <num>
#> 1:     [0,5)           95 0.09396637
#> 2:    [5,15)          204 0.20178042
#> 3:       15+          712 0.70425321
#>