65 lines
1.4 KiB
C
65 lines
1.4 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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int compute(int N) {
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int i_0, i_1;
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// claim space
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double **A = (double **)malloc(sizeof(double *) * N);
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for (i_0 = 0; i_0 < N; i_0++) {
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A[i_0] = (double *)malloc(sizeof(double) * N);
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}
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double *x = (double *)malloc(sizeof(double) * N);
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double *y = (double *)malloc(sizeof(double) * N);
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double *y_sol = (double *)malloc(sizeof(double) * N);
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// fill matrix and vector
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for (i_0 = 0; i_0 < N; i_0++) {
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x[i_0] = i_0 + 1;
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y_sol[i_0] = (i_0 + 1) * N;
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for (i_1 = 0; i_1 < N; i_1++) {
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A[i_0][i_1] = (i_0 + 1.0) / (i_1 + 1.0);
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}
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}
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// for (i_0 = 0; i_0 < N; i_0++){
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// printf("[ ");
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// for(i_1 = 0; i_1 < N; i_1++){
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// printf("%.3f ",A[i_0][i_1]);
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// }
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// printf("]");
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// printf("[ %.1f ] = [ %.1f ][ %.1f ]\n",x[i_0],y[i_0],y_sol[i_0]);
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// }
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// compute matrix-vector product
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for (i_0 = 0; i_0 < N; i_0++) {
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y[i_0] = 0;
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for (i_1 = 0; i_1 < N; i_1++) {
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y[i_0] += A[i_0][i_1] * x[i_1];
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}
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}
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// compare result to solution
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double sum = 0.0;
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for (i_0 = 0; i_0 < N; i_0++) {
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sum += (y[i_0] - y_sol[i_0]) * (y[i_0] - y_sol[i_0]);
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}
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return sum;
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}
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int main(int argc, char *argv[]) {
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int N;
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if (argc != 2) {
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N = 1000;
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} else {
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N = atoi(argv[1]); // Convert the argument to an integer
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}
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double err = compute(N);
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printf("Error for N = %d: %.8f\n", N, err);
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return 0;
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}
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