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| void lu_decomposition(double** A, double** L, double** U, int n) { | |
| for (int i = 0; i < n; i++) { | |
| for (int k = i; k < n; k++) { | |
| double sum = 0; | |
| for (int j = 0; j < i; j++) | |
| sum += (L[i][j] * U[j][k]); | |
| U[i][k] = A[i][k] - sum; | |
| } | |
| for (int k = i; k < n; k++) { | |
| if (i == k) | |
| L[i][i] = 1; | |
| else { | |
| double sum = 0; | |
| for (int j = 0; j < i; j++) | |
| sum += (L[k][j] * U[j][i]); | |
| L[k][i] = (A[k][i] - sum) / U[i][i]; | |
| } | |
| } | |
| } | |
| } | |
| int main() { | |
| int n = 400; | |
| double** A = (double**)malloc(n * sizeof(double*)); | |
| double** L = (double**)malloc(n * sizeof(double*)); | |
| double** U = (double**)malloc(n * sizeof(double*)); | |
| for (int i = 0; i < n; i++) { | |
| A[i] = (double*)malloc(n * sizeof(double)); | |
| L[i] = (double*)calloc(n, sizeof(double)); | |
| U[i] = (double*)calloc(n, sizeof(double)); | |
| } | |
| srand(42); | |
| for (int i = 0; i < n; i++) { | |
| for (int j = 0; j < n; j++) { | |
| A[i][j] = (double)(rand() % 100) / 10.0; | |
| } | |
| A[i][i] += n; | |
| } | |
| clock_t start = clock(); | |
| lu_decomposition(A, L, U, n); | |
| clock_t end = clock(); | |
| double time_spent = (double)(end - start) / CLOCKS_PER_SEC; | |
| printf("LU decomposition: %dx%d in %.6f seconds\n", n, n, time_spent); | |
| for (int i = 0; i < n; i++) { | |
| free(A[i]); | |
| free(L[i]); | |
| free(U[i]); | |
| } | |
| free(A); | |
| free(L); | |
| free(U); | |
| return 0; | |
| } | |