Added Welsh Powell graph coloring

tests/test_graphcoloring.cpp

@@ -0,0 +1,69 @@
+#include <config.h>
+
+#include <dune/common/fmatrix.hh>
+#include <dune/istl/bcrsmatrix.hh>
+#include <dune/istl/paamg/graph.hh>
+
+#include <opm/autodiff/GraphColoring.hpp>
+
+#define BOOST_TEST_MODULE GraphColoringTest
+#define BOOST_TEST_MAIN
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_CASE(TestWelschPowell)
+{
+    using Matrix = Dune::BCRSMatrix<Dune::FieldMatrix<double,1,1>>;
+    using Graph = Dune::Amg::MatrixGraph<Matrix>;
+    int N = 10;
+    Matrix matrix(N*N, N*N, 5, 0.4, Matrix::implicit);
+    for( int j = 0; j < N; j++)
+    {
+        for(int i = 0; i < N; i++)
+        {
+            auto index = j*10+i;
+            matrix.entry(index,index) = 1;
+
+            if ( i > 0 )
+            {
+                matrix.entry(index,index-1) = 1;
+            }
+            if ( i  < N - 1)
+            {
+                matrix.entry(index,index+1) = 1;
+            }
+
+            if ( j > 0 )
+            {
+                matrix.entry(index,index-N) = 1;
+            }
+            if ( j  < N - 1)
+            {
+                matrix.entry(index,index+N) = 1;
+            }
+
+        }
+    }
+    matrix.compress();
+
+    auto colorsTuple = Opm::colorVerticesWelshPowell(Graph(matrix));
+    const auto& colors = std::get<0>(colorsTuple);
+    auto noColors = std::get<1>(colorsTuple);
+    auto firstCornerColor = colors[0];
+    BOOST_CHECK(noColors == 2);
+
+    // Check for checkerboard coloring
+
+    for( int j = 0, index = 0; j < N; j++)
+    {
+        auto expectedColor = firstCornerColor;
+
+        for(int i = 0; i < N; i++)
+        {
+            BOOST_CHECK(colors[index]==expectedColor);
+            index++;
+            expectedColor = (expectedColor + 1) % 2;
+        }
+        firstCornerColor=(firstCornerColor + 1) % 2;
+    }
+}