some composition optimizations (#1913)

Author: zingale

EOS/eos_composition.H

@@ -58,28 +58,22 @@ void composition (T& state)
 
 #ifdef AUX_THERMO
 
-  state.mu_e = 1.0 / state.aux[iye];
+  state.mu_e = 1.0_rt / state.aux[iye];
   state.y_e = state.aux[iye];
   state.abar = state.aux[iabar];
   state.zbar = state.abar * state.y_e;
 
 #else
 
-  amrex::Real sum = 0;
+  state.y_e = 0.0_rt;
+  state.abar = 0.0_rt;
   for (int n = 0; n < NumSpec; n++) {
-    sum += state.xn[n] * zion[n] * aion_inv[n];
+    state.y_e += state.xn[n] * zion[n] * aion_inv[n];
+    state.abar += state.xn[n] * aion_inv[n];
   }
+  state.abar = 1.0_rt / state.abar;
 
-  state.mu_e = 1.0 / sum;
-  state.y_e = sum;
-
-  sum = 0;
-
-  for (int n = 0; n < NumSpec; n++) {
-    sum += state.xn[n] * aion_inv[n];
-  }
-
-  state.abar = 1.0 / sum;
+  state.mu_e = 1.0_rt / state.y_e;
   state.zbar = state.abar * state.y_e;
 #endif
 }

EOS/helmholtz/actual_eos.H

@@ -170,9 +170,6 @@ void apply_electrons (T& state)
     // assume complete ionization
     [[maybe_unused]] amrex::Real ytot1 = 1.0e0_rt / state.abar;
 
-    // define mu -- the total mean molecular weight including both electrons and ions
-    state.mu = 1.0e0_rt / (1.0e0_rt / state.abar + 1.0e0_rt / state.mu_e);
-
     // enter the table with ye*den
     amrex::Real din = state.y_e * state.rho;
 
@@ -1129,6 +1126,9 @@ void finalize_state (I input, T& state,
 {
     using namespace helmholtz;
 
+    // define mu -- the total mean molecular weight including both electrons and ions
+    state.mu = 1.0e0_rt / (1.0e0_rt / state.abar + 1.0e0_rt / state.mu_e);
+
     // Calculate some remaining derivatives
     if constexpr (has_pressure<T>::value) {
         state.dpde = state.dpdT / state.dedT;