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- #include <stdio.h>
- #include <time.h>
- #include <math.h>
- void lorenz(const double *x, double *restrict y) {
- y[0] = 10.0 * (x[1] - x[0]);
- y[1] = 28.0 * x[0] - x[1] - x[0] * x[2];
- y[2] = x[0] * x[1] - (8.0 / 3.0) * x[2];
- }
- int main(int argc, const char *argv[])
- {
- const int nb_steps = 20000000;
- const double h = 1.0e-10;
- const double h2 = 0.5 * h;
- const double nb_loops = 21;
- double x[3];
- double y[3];
- double f1[3];
- double f2[3];
- double f3[3];
- double f4[3];
- double min_time = 1E6;
- clock_t begin, end;
- double time_spent;
-
- for (int j = 0; j < nb_loops; j++) {
- x[0] = 8.5;
- x[1] = 3.1;
- x[2] = 1.2;
- begin = clock();
- for (int k = 0; k < nb_steps; k++) {
- lorenz(x, f1);
- for (int i = 0; i < 3; i++) {
- y[i] = x[i] + h2 * f1[i];
- }
- lorenz(y, f2);
- for (int i = 0; i < 3; i++) {
- y[i] = x[i] + h2 * f2[i];
- }
- lorenz(y, f3);
- for (int i = 0; i < 3; i++) {
- y[i] = x[i] + h * f3[i];
- }
- lorenz(y, f4);
- for (int i = 0; i < 3; i++) {
- x[i] = x[i] + h * (f1[i] + 2 * (f2[i] + f3[i]) + f4[i]) / 6.0;
- }
- }
- end = clock();
- min_time = fmin(min_time, (double)(end-begin)/CLOCKS_PER_SEC);
- printf("Result: %f\t runtime: %f\n", x[0], (double)(end-begin)/CLOCKS_PER_SEC);
- }
- printf("Minimal Runtime: %f\n", min_time);
-
- return 0;
- }
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