sheet 4

sheet4/A/.vscode/settings.json

@@ -0,0 +1,6 @@
+{
+    "files.associations": {
+        "ostream": "cpp",
+        "iostream": "cpp"
+    }
+}

sheet4/A/Makefile

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+#
+# use GNU-Compiler tools
+COMPILER=GCC_
+# alternatively from the shell
+# export COMPILER=GCC_
+# or, alternatively from the shell
+# make COMPILER=GCC_
+
+# use Intel compilers
+#COMPILER=ICC_
+
+# use PGI compilers
+# COMPILER=PGI_
+
+
+SOURCES = main.cpp 
+OBJECTS = $(SOURCES:.cpp=.o)
+
+PROGRAM	= main.${COMPILER}
+
+# uncomment the next to lines for debugging and detailed performance analysis
+CXXFLAGS += -g
+LINKFLAGS += -g
+# do not use -pg with PGI compilers
+
+ifndef COMPILER
+  COMPILER=GCC_
+endif
+
+include ../${COMPILER}default.mk
+$(PROGRAM): $(OBJECTS)
+	$(CXX) $(CXXFLAGS) $(OBJECTS) -llapacke -lopenblas -o $(PROGRAM)

sheet4/A/main.cpp

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+#include <iostream>
+#include <sstream>
+#include <vector>
+#include <lapacke.h>
+using namespace std;
+
+int main()
+{   
+    int n = 10;
+    unsigned int nodes = n+1;
+    int rhs = 1;
+    double a = 1.0;
+    double alpha = 2.0;
+    double gB = 1.0;
+
+    double d = n + a/3.0/n;
+    double s = - n + a / 6.0 / n;
+
+    cout << d << endl;
+    cout << s << endl;
+
+    //Lapacke overwrites upper/lower diagonal so store twice 
+    vector<double> upperdiagonal(n,s);
+    vector<double> lowerdiagonal(n,s);
+    vector<double> diagonal(nodes,2*d);
+    vector<double> F(nodes,1.0/n);
+
+    diagonal[0]=1.0;
+    diagonal[n]=d+alpha;
+
+    upperdiagonal[0] = 0.0;
+    //
+
+    F[0] = 0;
+    F[n]= 1.0/n/2.0 +alpha*gB;
+    
+
+    //Tridiagonal
+    LAPACKE_dgtsv(LAPACK_COL_MAJOR,nodes,rhs,lowerdiagonal.data(),diagonal.data(),upperdiagonal.data(),F.data(),nodes);
+    
+
+    cout << "Solution u_h at nodes x_1..x_" << n << ":\n";
+    for (unsigned int i = 0; i < nodes; ++i) {
+
+        double xi = double(i) /double(n);
+        cout << "u_h(" << xi << ") = " << F[i] << "\n";
+        // F will be overwritten with sol
+    }
+
+    return 0;
+
+    
+}