From 2810db0d526f2147b2cd7e1676b13d53cdab8cb0 Mon Sep 17 00:00:00 2001
From: philippun <philippungrund@icloud.com>
Date: Thu, 10 Aug 2023 14:21:00 +0200
Subject: [PATCH] added BTCSv2.cpp

---
 include/tug/Boundary.hpp |  1 -
 include/tug/Grid.hpp     |  1 +
 src/BTCSv2.cpp           | 51 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 src/BTCSv2.cpp

diff --git a/include/tug/Boundary.hpp b/include/tug/Boundary.hpp
index 98d0181..2173180 100644
--- a/include/tug/Boundary.hpp
+++ b/include/tug/Boundary.hpp
@@ -7,7 +7,6 @@
 #ifndef BOUNDARY_H_
 #define BOUNDARY_H_
 
-#include <Eigen/Core>
 #include <cstddef>
 #include "Grid.hpp"
 
diff --git a/include/tug/Grid.hpp b/include/tug/Grid.hpp
index 59f8ed0..a87325e 100644
--- a/include/tug/Grid.hpp
+++ b/include/tug/Grid.hpp
@@ -6,6 +6,7 @@
  */
 
 #include <Eigen/Core>
+#include <Eigen/Sparse>
 
 using namespace Eigen;
 
diff --git a/src/BTCSv2.cpp b/src/BTCSv2.cpp
new file mode 100644
index 0000000..4977060
--- /dev/null
+++ b/src/BTCSv2.cpp
@@ -0,0 +1,51 @@
+#include "TugUtils.hpp"
+#include <tug/Boundary.hpp>
+
+using namespace Eigen;
+
+
+// calculates arithmetic or harmonic mean of alpha between two cells
+static double calcAlphaIntercell(double &alpha1, double &alpha2, bool useHarmonic = true) {
+    if (useHarmonic) {
+        return double(2) / ((double(1)/alpha1) + (double(1)/alpha2));
+    } else {
+        return 0.5 * (alpha1 + alpha2);
+    }
+}
+
+
+static MatrixXd createCoeffMatrix(Grid &grid, int rowIndex, double sx) {
+
+    // square matrix of column^2 dimension for the coefficients
+    int dim = grid.getCol();
+    SparseMatrix<double, RowMajor> cm(dim, dim);
+
+    // top left
+    cm.coeffRef(0,0) = 1 + sx * (calcAlphaIntercell(grid.getAlphaX()(rowIndex,0), grid.getAlphaX()(rowIndex,1)));
+
+
+}
+
+
+// BTCS solution for 1D grid
+static void BTCS_1D(Grid &grid, Boundary &bc, double &timestep) {
+
+}
+
+
+// BTCS solution for 2D grid
+static void BTCS_2D(Grid &grid, Boundary &bc, double &timestep) {
+
+}
+
+
+// entry point; differentiate between 1D and 2D grid
+static void BTCS(Grid &grid, Boundary &bc, double &timestep) {
+    if (grid.getDim() == 1) {
+        BTCS_1D(grid, bc, timestep);
+    } else if (grid.getDim() == 2) {
+        BTCS_2D(grid, bc, timestep);
+    } else {
+        throw_invalid_argument("Error: Only 1- and 2-dimensional grids are defined!");
+    }
+}
\ No newline at end of file