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some small optimizations to Rosenbrock #2084

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some small optimizations to Rosenbrock #2084

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24 changes: 14 additions & 10 deletions integration/Rosenbrock/rosenbrock_integrator.H
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Original file line number Diff line number Diff line change
Expand Up @@ -157,12 +157,14 @@ bool species_change_valid ([[maybe_unused]] const rosenbrock_t<int_neqs>& rstate
#ifdef STRANG
constexpr amrex::Real increase_change_factor = 4.0_rt;
constexpr amrex::Real decrease_change_factor = 0.25_rt;
const amrex::Real reject_threshold = integrator_rp::X_reject_buffer * rstate.atol_spec;

for (int i = 1; i <= NumSpec; ++i) {
if (std::abs(rstate.y(i)) > integrator_rp::X_reject_buffer * rstate.atol_spec &&
std::abs(rstate.ynew(i)) > integrator_rp::X_reject_buffer * rstate.atol_spec &&
(std::abs(rstate.ynew(i)) > increase_change_factor * std::abs(rstate.y(i)) ||
std::abs(rstate.ynew(i)) < decrease_change_factor * std::abs(rstate.y(i)))) {
const amrex::Real y_abs = std::abs(rstate.y(i));
const amrex::Real ynew_abs = std::abs(rstate.ynew(i));
if (y_abs > reject_threshold && ynew_abs > reject_threshold &&
(ynew_abs > increase_change_factor * y_abs ||
ynew_abs < decrease_change_factor * y_abs)) {
return false;
}
}
Expand Down Expand Up @@ -236,6 +238,7 @@ void evaluate_jacobian (BurnT& state, rosenbrock_t<int_neqs>& rstate, const amre
}

constexpr amrex::Real UROUND = std::numeric_limits<amrex::Real>::epsilon();
const amrex::Real sqrt_roundoff = std::sqrt(UROUND);
amrex::Array1D<amrex::Real, 1, int_neqs> ewt;
amrex::Array1D<amrex::Real, 1, int_neqs> ybase;

Expand All @@ -259,7 +262,7 @@ void evaluate_jacobian (BurnT& state, rosenbrock_t<int_neqs>& rstate, const amre

for (int j = 1; j <= int_neqs; ++j) {
const amrex::Real yj = ybase(j);
const amrex::Real R = amrex::max(std::sqrt(UROUND) * std::abs(yj), R0 / ewt(j));
const amrex::Real R = amrex::max(sqrt_roundoff * std::abs(yj), R0 / ewt(j));
for (int n = 1; n <= int_neqs; ++n) {
rstate.y(n) = ybase(n);
}
Expand Down Expand Up @@ -382,6 +385,9 @@ int rosenbrock_integrator (BurnT& state, rosenbrock_t<integrator_neqs<BurnT>()>&
amrex::Real x = rstate.t;
amrex::Array1D<amrex::Real, 1, int_neqs> rhs_tmp;

const amrex::Real error_exponent = 1.0_rt / (integrator_rp::h211b_b * integrator_rp::h211b_k);
const amrex::Real history_exponent = -1.0_rt / integrator_rp::h211b_b;

// main evolution loop

// within this loop, x will be the current time and h will be the
Expand Down Expand Up @@ -533,11 +539,9 @@ int rosenbrock_integrator (BurnT& state, rosenbrock_t<integrator_neqs<BurnT>()>&
constexpr amrex::Real err_min = 1.e-10_rt;
amrex::Real err = rosenbrock::error_norm(rstate);
amrex::Real controller_fac = amrex::Clamp(
std::pow(1.0_rt / amrex::max(err, err_min),
1.0_rt / (integrator_rp::h211b_b * integrator_rp::h211b_k)) *
std::pow(1.0_rt / amrex::max(errold, err_min),
1.0_rt / (integrator_rp::h211b_b * integrator_rp::h211b_k)) *
std::pow(facold, -1.0_rt / integrator_rp::h211b_b),
std::pow(1.0_rt / amrex::max(err, err_min), error_exponent) *
std::pow(1.0_rt / amrex::max(errold, err_min), error_exponent) *
std::pow(facold, history_exponent),
integrator_rp::h211b_fac_min, integrator_rp::h211b_fac_max);
facold = controller_fac;
errold = err;
Expand Down
2 changes: 1 addition & 1 deletion integration/Rosenbrock/rosenbrock_type.H
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
// When checking the integration time to see if we're done,
// be careful with roundoff issues.

const amrex::Real timestep_safety_factor = 1.0e-4_rt;
constexpr amrex::Real timestep_safety_factor = 1.0e-4_rt;

template <int int_neqs>
struct rosenbrock_t {
Expand Down
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