From 779ef0e8c3aaeebde6e6400701c4daed644201b2 Mon Sep 17 00:00:00 2001
From: Ian Bell <ian.h.bell@gmail.com>
Date: Tue, 23 Aug 2016 20:01:49 -0600
Subject: [PATCH] First tests for derivatives of am for VTPR

@JonWel, looks like there is some more debugging to be done here :(
---
 src/Backends/Cubics/VTPRBackend.cpp | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/Backends/Cubics/VTPRBackend.cpp b/src/Backends/Cubics/VTPRBackend.cpp
index ea454037..98f86ae8 100644
--- a/src/Backends/Cubics/VTPRBackend.cpp
+++ b/src/Backends/Cubics/VTPRBackend.cpp
@@ -77,3 +77,31 @@ const UNIFAQLibrary::UNIFAQParameterLibrary & CoolProp::VTPRBackend::LoadLibrary
     }
     return lib;
 }
+
+#ifdef ENABLE_CATCH
+#include "catch.hpp"
+
+#include "Backends/Cubics/CubicBackend.h"
+
+using namespace CoolProp;
+
+TEST_CASE("VTPR test","[VTPR]")
+{
+    shared_ptr<VTPRBackend> VTPR(new VTPRBackend(strsplit("Ethane&n-Propane&n-Butane",'&')));
+    std::vector<double> z(3); z[0] = 0.1; z[1] = 0.2; z[2] = 0.7;
+    VTPR->set_mole_fractions(z);
+    
+    SECTION("dam_dxi"){
+        shared_ptr<AbstractCubic> cubic = VTPR->get_cubic();
+        double tau = 0.001, dz = 1e-6;
+        std::vector<double> zp = z, zm = z;
+        zp[0] += dz; zm[0] -= dz;
+        
+        double dam_dxi_num = (cubic->am_term(tau, zp, 0) - cubic->am_term(tau, zm, 0))/(2*dz);
+        double dam_dxi_ana = cubic->d_am_term_dxi(tau, z, 0, 0, XN_INDEPENDENT);
+        double diff = dam_dxi_num-dam_dxi_ana;
+        CHECK(std::abs(diff)<1e-6);
+    }
+}
+
+#endif