From 94d3e79a8617f88dc0219cfdeedfa3147833719d Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Mon, 24 Jun 2019 14:43:36 +0200
Subject: Initialize at openlb-1-3

---
 src/core/finiteDifference.h | 80 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 src/core/finiteDifference.h

(limited to 'src/core/finiteDifference.h')

diff --git a/src/core/finiteDifference.h b/src/core/finiteDifference.h
new file mode 100644
index 0000000..3e2da30
--- /dev/null
+++ b/src/core/finiteDifference.h
@@ -0,0 +1,80 @@
+/*  This file is part of the OpenLB library
+ *
+ *  Copyright (C) 2006, 2007 Jonas Latt
+ *  E-mail contact: info@openlb.net
+ *  The most recent release of OpenLB can be downloaded at
+ *  <http://www.openlb.net/>
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License
+ *  as published by the Free Software Foundation; either version 2
+ *  of the License, or (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public
+ *  License along with this program; if not, write to the Free
+ *  Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA  02110-1301, USA.
+*/
+
+#ifndef FINITE_DIFFERENCE_H
+#define FINITE_DIFFERENCE_H
+
+namespace olb {
+
+namespace fd {
+
+/// Second-order central gradient (u_p1 = u(x+1))
+template<typename T>
+T centralGradient(T u_p1, T u_m1)
+{
+  return (u_p1 - u_m1) / (T)2;
+}
+
+/// Second-order asymmetric gradient (u_1 = u(x+1))
+template<typename T>
+T boundaryGradient(T u_0, T u_1, T u_2)
+{
+  return (-(T)3*u_0 + (T)4*u_1 - (T)1*u_2) / (T)2;
+}
+
+/// Forward second-order first derivative
+template<typename T>
+T FSGradient(T u_0, T u_1, T u_2)
+{
+  T result = boundaryGradient(u_0, u_1, u_2);
+  return result;
+}
+
+/// Backward second-order first derivative
+template<typename T>
+T BSGradient(T u_0, T u_1, T u_2)
+{
+  T result = -1*boundaryGradient(u_0, u_1, u_2);
+  return result;
+}
+
+/// Value at u_0 for which asymmetric gradient is zero (u_1 = u(x+1))
+template<typename T>
+T boundaryZeroGradient(T u_1, T u_2)
+{
+  return (T)4/(T)3*u_1 - (T)1/(T)3*u_2;
+}
+
+/// Linear interpolation (yields u0 at pos=0 and u1 at pos=1)
+template<typename T>
+T linearInterpolate(T u_0, T u_1, T pos)
+{
+  return ((T)1-pos)*u_0 + pos*u_1;
+}
+
+}  // namespace fd
+
+}  // namespace olb
+
+
+#endif
-- 
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