tests/testthat/test-resource_semichemostat.R

In drfinlayscott/mizer: Dynamic Multi-Species Size Spectrum Modelling

test_that("resource_semichemostat preserves steady state", {
    # Set resource parameters so that we are at steady state
    params <- newTraitParams()
    params <- setResource(params,
                          resource_capacity = 2 * initialNResource(params),
                          resource_dynamics = "resource_semichemostat")
    x <- resource_semichemostat(params, 
                                n = params@initial_n,
                                n_pp = params@initial_n_pp,
                                n_other = params@initial_n_other,
                                rates = getRates(params),
                                t = 0, dt = 0.1,
                                resource_capacity = params@cc_pp,
                                resource_rate = params@rr_pp)
    expect_equal(x, params@initial_n_pp,
                 tolerance = 1e-15,
                 ignore_attr = TRUE)
})


test_that("resource_semichemostat evolves towards steady state", {
    # This might go wrong if numerical errors are too large. This in turn
    # might happen when the rates are small. To achieve that we
    # reduce plankton mortality to a small value by scaling gamma down by
    # a large factor s and simultaneously scaling up the plankton abundance
    # so as to keep the income of the fish constant.
    s <- 1e10
    params <- newTraitParams()
    species_params(params)$gamma <- species_params(params)$gamma / s
    initialNResource(params) <- initialNResource(params) * s
    # Set resource parameters so that we are at steady state
    params <- setResource(params,
                          resource_capacity = 2 * initialNResource(params),
                          resource_rate = getResourceMort(params),
                          balance = FALSE)
    # Now perturb a bit away from steady state
    n_pp_pert <- params@initial_n_pp * (1 + 1e-10)
    # run the dynamics for one time step and check that the perturbation has
    # not grown
    x <- resource_semichemostat(params, 
                                n = params@initial_n,
                                n_pp = n_pp_pert,
                                n_other = params@initial_n_other,
                                rates = getRates(params),
                                t = 0, dt = 0.1,
                                resource_capacity = params@cc_pp,
                                resource_rate = params@rr_pp)
    expect_lte(max(abs(x - n_pp_pert)), 0)
})


test_that("balance_resource_semichemostat works", {
    # semichemostat rate
    sc <- function(params) {
        r <- params@rr_pp
        c <- params@cc_pp
        N <- params@initial_n_pp
        mu <- getResourceMort(params)
        N_steady <- r * c / (mu + r)
        sel <- (mu + r) > 0
        all.equal(N_steady[sel], N[sel])
    }
    
    params <- NS_params
    
    # setting rate
    rate <- getResourceMort(params)
    params <- setResource(params, resource_rate = rate,
                          resource_dynamics = "resource_semichemostat")
    expect_identical(params@rr_pp, rate)
    expect_true(sc(params))
    
    # setting capacity
    capacity <- params@cc_pp * 2
    p1 <- setResource(params, resource_capacity = capacity)
    expect_identical(p1@cc_pp, capacity)
    expect_true(sc(p1))
})