rounding issues w/ mass functions

[smwindecker]

discretised probability mass functions need to sum to 1, but sometimes don't because of rounding issues

[AugustHao]

I found this code from Nick for a different purpose, I think adding a normalisation might be all we need?

# greta function for the probability mass function of a discretised lognormal
# distribution, truncated at max_days
discrete_lognormal_pmf <- function(days, meanlog, sdlog, max_days) {

  lower <- lognormal_cdf(
    q = days - 1,
    meanlog = meanlog,
    sdlog = sdlog
  )

  upper <- lognormal_cdf(
    q = days,
    meanlog = meanlog,
    sdlog = sdlog
  )

  normalisation <- lognormal_cdf(
    q = max_days,
    meanlog = meanlog,
    sdlog = sdlog
  )

  pmf_unnormalised <- upper - lower
  pmf_unnormalised[days > max_days] <- 0
  pmf <- pmf_unnormalised / normalisation

  pmf

[AugustHao]

fixed in #4a6bcc0