MeanField/tests/physics/barotrope.cpp

#include <array>
#include <cmath>
#include <limits>

#include <catch2/catch_test_macros.hpp>
#include <catch2/matchers/catch_matchers_floating_point.hpp>

import mean_field;
import test_helpers;

TEST_CASE(
    "Polytropic Barotrope Satisfies Its Analytic Identities",
    tags::hydro &tags::unit &tags::barotrope
) {
    constexpr double polytropic_index    = 3.0;
    constexpr double polytropic_constant = 1.5;

    const mean_field::physics::PolytropicBarotrope barotrope(polytropic_index, polytropic_constant);

    const std::array<double, 5> densities{1.0e-6, 1.0e-3, 0.1, 0.7, 2.0};

    for (const double density : densities) {
        const double pressure               = barotrope.pressure_from_density(density);

        const double enthalpy               = barotrope.enthalpy_from_density(density);

        const double reconstructed_density  = barotrope.density_from_enthalpy(enthalpy);

        const double reconstructed_pressure = barotrope.pressure_from_enthalpy(enthalpy);

        CHECK_THAT(reconstructed_density, Catch::Matchers::WithinRel(density, 2.0e-14));

        CHECK_THAT(reconstructed_pressure, Catch::Matchers::WithinRel(pressure, 2.0e-14));

        CHECK_THAT(pressure, Catch::Matchers::WithinRel(density * enthalpy / (polytropic_index + 1.0), 2.0e-14));

        CHECK_THAT(barotrope.pressure_derivative_from_enthalpy(enthalpy), Catch::Matchers::WithinRel(density, 2.0e-14));

        CHECK_THAT(
            barotrope.pressure_derivative_from_density(density),
            Catch::Matchers::WithinRel(enthalpy / polytropic_index, 2.0e-14)
        );
    }
}

TEST_CASE(
    "Polytropic Barotrope Derivatives Match Centered Differences",
    tags::hydro &tags::jacobian &tags::unit &tags::barotrope
) {
    const mean_field::physics::PolytropicBarotrope barotrope(3.0, 1.5);

    const std::array<double, 4> enthalpies{0.05, 0.2, 0.7, 1.4};

    for (const double enthalpy : enthalpies) {
        const double step = 1.0e-6 * std::max(1.0, enthalpy);

        const double density_difference =
            (barotrope.density_from_enthalpy(enthalpy + step) - barotrope.density_from_enthalpy(enthalpy - step)) /
            (2.0 * step);

        const double pressure_difference =
            (barotrope.pressure_from_enthalpy(enthalpy + step) - barotrope.pressure_from_enthalpy(enthalpy - step)) /
            (2.0 * step);

        CHECK_THAT(
            density_difference,
            Catch::Matchers::WithinRel(barotrope.density_derivative_from_enthalpy(enthalpy), 5.0e-10)
        );

        CHECK_THAT(
            pressure_difference,
            Catch::Matchers::WithinRel(barotrope.pressure_derivative_from_enthalpy(enthalpy), 5.0e-10)
        );
    }
}

TEST_CASE(
    "Polytropic Barotrope Has An Exact Zero Density Surface",
    tags::hydro &tags::unit &tags::barotrope
) {
    const mean_field::physics::PolytropicBarotrope barotrope(3.0, 1.5);

    CHECK(barotrope.density_from_enthalpy(-1.0) == 0.0);
    CHECK(barotrope.density_from_enthalpy(0.0) == 0.0);

    CHECK(barotrope.pressure_from_enthalpy(-1.0) == 0.0);
    CHECK(barotrope.pressure_from_enthalpy(0.0) == 0.0);

    CHECK(barotrope.density_derivative_from_enthalpy(-1.0) == 0.0);

    CHECK(barotrope.density_derivative_from_enthalpy(0.0) == 0.0);

    CHECK(barotrope.pressure_derivative_from_enthalpy(0.0) == 0.0);
}

TEST_CASE(
    "Polytropic Barotrope Rejects Invalid Material Parameters",
    tags::hydro &tags::unit
) {
    CHECK_THROWS_AS(mean_field::physics::PolytropicBarotrope(0.5, 1.0), std::invalid_argument);

    CHECK_THROWS_AS(mean_field::physics::PolytropicBarotrope(3.0, 0.0), std::invalid_argument);

    CHECK_THROWS_AS(
        mean_field::physics::PolytropicBarotrope(std::numeric_limits<double>::infinity(), 1.0), std::invalid_argument
    );

    const mean_field::physics::PolytropicBarotrope barotrope(3.0, 1.0);

    CHECK_THROWS_AS(barotrope.pressure_from_density(-1.0), std::domain_error);

    CHECK_THROWS_AS(barotrope.enthalpy_from_density(-1.0), std::domain_error);
}