get-performance-parameters.R

get_perf_params <- function(world_record_perf, able_bodied_perf, limit,
                             type = "running") {
  # sum of squares around fixed point
  rss <- function(a, b, world_record_perf, able_bodied_perf, limit) {
    (1000 - b * log(a / (world_record_perf - limit))) ** 2 +
    (0    - b * log(a / (able_bodied_perf - limit))) ** 2
  }

  stopifnot(type %in% c("running", "jumping"))
  a_starting <- ifelse(type == "running", 5, -5)
  b_starting <- 100

 optim_results <- optim(c(a_starting, b_starting),
                        function(params) rss(params[1], params[2],
                                             world_record_perf,
                                             able_bodied_perf, limit))
 list(a = optim_results$par[1], b = optim_results$par[2], limit = limit,
      optim_results = optim_results)
}