From a38ff14efeb203dcb74817e9f2e73c46d501d8da Mon Sep 17 00:00:00 2001
From: psharda <piyush.suneet@gmail.com>
Date: Wed, 2 Aug 2023 16:14:04 +0200
Subject: [PATCH] define fundamental derivative G

---
 EOS/gamma_law/actual_eos.H | 2 +-
 interfaces/eos_type.H      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/EOS/gamma_law/actual_eos.H b/EOS/gamma_law/actual_eos.H
index 9274baf447..a225c7d037 100644
--- a/EOS/gamma_law/actual_eos.H
+++ b/EOS/gamma_law/actual_eos.H
@@ -265,7 +265,7 @@ void actual_eos (I input, T& state)
 
             // sound speed
             state.cs = std::sqrt(eos_gamma * state.p * rhoinv);
-            state.d2pdr2_s = state.cs * state.cs * (std::pow(state.cs, 2) / state.p - rhoinv);
+            state.G = 0.5 * (1.0 + (rho / state.p) * state.cs * state.cs);
         }
     }
 
diff --git a/interfaces/eos_type.H b/interfaces/eos_type.H
index 9267c97d2f..5e030a26fb 100644
--- a/interfaces/eos_type.H
+++ b/interfaces/eos_type.H
@@ -27,7 +27,7 @@ struct eos_t:eos_base_t {
     amrex::Real dsdr{};
     amrex::Real dpde{};
     amrex::Real dpdr_e{};
-    amrex::Real d2pdr2_s{};
+    amrex::Real G{}; // fundmental derivative (Thompson 1971)
 
     amrex::Real cv{};
     amrex::Real cp{};
@@ -146,7 +146,7 @@ struct chem_eos_t:eos_base_t {
     amrex::Real dpdr_e{};
     amrex::Real dedT{};
     amrex::Real dedr{};
-    amrex::Real d2pdr2_s{};
+    amrex::Real G{};
 
     amrex::Real mu{};
     amrex::Real cs{};