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CppCheck expm1 log1p HeatRecovery #10880

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Jan 9, 2025
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CppCheck expm1 log1p HeatRecovery #10880

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8 changes: 4 additions & 4 deletions src/EnergyPlus/HeatRecovery.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -3133,7 +3133,7 @@ namespace HeatRecovery {
} break;
case HXConfiguration::CrossFlowBothUnmixed: { // CROSS FLOW BOTH UNMIXED
Temp = Z * std::pow(NTU, -0.22);
Eps = 1.0 - std::exp((std::exp(-NTU * Temp) - 1.0) / Temp);
Eps = 1.0 - std::exp(std::expm1(-NTU * Temp) / Temp);
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@Myoldmopar Myoldmopar Jan 9, 2025 •
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It's mildly confusing to me that

expm1(n) is the same as exp(n) - 1

but

log1p(n) is the same as log(n + 1).

I understand the difference, but at first glance I thought maybe that was the cause of diffs here.

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@rraustad rraustad Jan 9, 2025 •
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These are supposed to be more precise. So consider these improvements that could possibly change the answer slightly.

log1p(n) = log(1 + n)

I did these individually by module because there were diffs when I combined them all in 1 branch and I wanted to be sure which change caused which diffs.

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Indeed it all makes sense. And it really can't be worth the time to investigate the diffs further. You've done a great job already, I feel comfortable merging the three log/exp branches, as it is crystal clear that they are just precision improvements.

} break;
case HXConfiguration::CrossFlowOther: { // CROSS FLOW, Cmax MIXED, Cmin UNMIXED
Eps = (1.0 - std::exp(-Z * (1.0 - std::exp(-NTU)))) / Z;
Expand Down Expand Up @@ -3221,13 +3221,13 @@ namespace HeatRecovery {
}
} break;
case HXConfiguration::ParallelFlow: { // PARALLEL FLOW
NTU = -std::log(-Eps - Eps * Z + 1.0) / (Z + 1.0);
NTU = -std::log1p(-Eps - Eps * Z) / (Z + 1.0);
} break;
case HXConfiguration::CrossFlowBothUnmixed: { // CROSS FLOW BOTH UNMIXED
NTU = GetNTUforCrossFlowBothUnmixed(state, Eps, Z);
} break;
case HXConfiguration::CrossFlowOther: { // CROSS FLOW, Cmax MIXED, Cmin UNMIXED
NTU = -std::log(1.0 + std::log(1.0 - Eps * Z) / Z);
NTU = -std::log1p(std::log(1.0 - Eps * Z) / Z);
} break;
default: {
ShowFatalError(state, format("HeatRecovery: Illegal flow arrangement in CalculateNTUfromEpsAndZ, Value={}", FlowArr));
Expand Down Expand Up @@ -3273,7 +3273,7 @@ namespace HeatRecovery {
int SolFla; // Flag of solver
Real64 constexpr NTU0(0.0); // lower bound for NTU
Real64 constexpr NTU1(50.0); // upper bound for NTU
auto f = [Eps, Z](Real64 const NTU) { return 1.0 - std::exp((std::exp(-std::pow(NTU, 0.78) * Z) - 1.0) / Z * std::pow(NTU, 0.22)) - Eps; };
auto f = [Eps, Z](Real64 const NTU) { return 1.0 - std::exp(std::expm1(-std::pow(NTU, 0.78) * Z) / Z * std::pow(NTU, 0.22)) - Eps; };
General::SolveRoot(state, Acc, MaxIte, SolFla, NTU, f, NTU0, NTU1);

if (SolFla == -2) {
Expand Down
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