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parallele_spaltenzerlegung.cpp

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+#include <vector>
+#include <chrono>
+#include <iostream>
+#include <omp.h>
+#include <cstdlib>
+#include <ctime>
+
+// Zufallsmatrizen erzeugen
+void generateRandomMatrices(int n,
+                            std::vector<std::vector<double>>& A,
+                            std::vector<std::vector<double>>& B)
+{
+    std::srand(static_cast<unsigned int>(std::time(nullptr)));
+    A.resize(n, std::vector<double>(n));
+    B.resize(n, std::vector<double>(n));
+
+    for (int i = 0; i < n; ++i)
+        for (int j = 0; j < n; ++j)
+        {
+            A[i][j] = static_cast<double>(rand()) / RAND_MAX * 10.0;
+            B[i][j] = static_cast<double>(rand()) / RAND_MAX * 10.0;
+        }
+}
+
+// Serielle Matrizenmultiplikation
+std::vector<std::vector<double>> matmul_serial(
+    const std::vector<std::vector<double>>& A,
+    const std::vector<std::vector<double>>& B)
+{
+    int n = A.size();
+    int m = B[0].size();
+    int p = B.size();
+    std::vector<std::vector<double>> C(n, std::vector<double>(m, 0.0));
+
+    for (int i = 0; i < n; ++i)
+        for (int j = 0; j < m; ++j)
+            for (int k = 0; k < p; ++k)
+                C[i][j] += A[i][k] * B[k][j];
+
+    return C;
+}
+
+// Spaltenparallel (Column-parallel)
+std::vector<std::vector<double>> matmul_column_parallel(
+    const std::vector<std::vector<double>>& A,
+    const std::vector<std::vector<double>>& B)
+{
+    int n = A.size();
+    int m = B[0].size();
+    int p = B.size();
+    std::vector<std::vector<double>> C(n, std::vector<double>(m, 0.0));
+
+#pragma omp parallel for
+    for (int j = 0; j < m; ++j)      // Spalten parallel
+        for (int i = 0; i < n; ++i)
+            for (int k = 0; k < p; ++k)
+                C[i][j] += A[i][k] * B[k][j];
+
+    return C;
+}
+
+// -----------------------------
+int main()
+{
+    int N = 500;
+    std::vector<std::vector<double>> A, B;
+    generateRandomMatrices(N, A, B);
+
+    // Serielle Version
+    auto start = std::chrono::steady_clock::now();
+    auto C_serial = matmul_serial(A, B);
+    auto end = std::chrono::steady_clock::now();
+    std::cout << "Serial multiplication took: "
+              << std::chrono::duration<double>(end - start).count() << "s\n";
+
+    // Spaltenparallel
+    start = std::chrono::steady_clock::now();
+    auto C_col = matmul_column_parallel(A, B);
+    end = std::chrono::steady_clock::now();
+    std::cout << "Column-parallel multiplication took: "
+              << std::chrono::duration<double>(end - start).count() << "s\n";
+
+    // Vergleich
+    for (int i = 0; i < N; ++i)
+        for (int j = 0; j < N; ++j)
+            if (C_serial[i][j] != C_col[i][j])
+            {
+                std::cout << "Mismatch at " << i << "," << j << "\n";
+                return 1;
+            }
+
+    std::cout << "All results match!\n";
+    return 0;
+}