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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <math.h>
  4.  
  5. void det_calc(double *matrix, int pivot[], int dim){
  6.     int m, n, p;
  7.     double *mat, *row, *col, max;
  8.     mat = matrix;
  9.     for (p = 0; p < dim; mat += dim, p++){ // Get the pivot
  10.         pivot[p] = p;
  11.         max = fabs(*(mat + p));
  12.         row = mat + dim;
  13.         for (n = p + 1; n < dim; n++, row += dim){
  14.             if (max < fabs(*(row + p))){
  15.                 max = fabs(*(row + p));
  16.                 pivot[p] = n;
  17.                 col = row;
  18.             }
  19.         }
  20.         if (pivot[p] != p) // If pivot is diff from current row, swap
  21.             for (n = 0; n < dim; n++){
  22.                 max = *(mat + n);
  23.                 *(mat + n) = *(col + n);
  24.                 *(col + n) = max;
  25.             }
  26.         if (*(mat + p) == 0) return; // Singular matrix
  27.         row = mat + dim;
  28.         for (m = p + 1; m < dim; row += dim, m++) // Get lower triangular matrix
  29.             *(row + p) /= *(mat + p);
  30.         row = mat + dim;
  31.         for (m = p + 1; m < dim; row += dim, m++) // Update matrix
  32.             for (n = p + 1; n < dim; n++)
  33.                 *(row + n) -= *(row + p) * *(mat + n);
  34.     }
  35. }
  36.  
  37. int main(void){
  38.     int dim;
  39.     double result = 1.0;
  40.     char line[100];
  41.     char *p = line, *beginning = p, *end;
  42.     fgets(line, sizeof(line), stdin); // Get the first number
  43.     sscanf(line, "%d", &dim); // Convert to int
  44.     double matrix[dim][dim];
  45.     int pivot[dim]; // Array to track pivot
  46.     for (int i = 0; i < dim; i++){
  47.         fgets(line, sizeof(line), stdin); // Get next line
  48.         while (*p){ // Read until end of line
  49.             for (int j = 0; j < dim; j++)
  50.                 matrix[i][j] = strtod(p, &end); // Convert to double
  51.             p++;
  52.         }
  53.         p = beginning;
  54.     }
  55.     det_calc(&matrix[0][0], pivot, dim);
  56.     for(int i = 0; i < dim; i++) result *= matrix[i][i];
  57.     printf("%f", result);
  58.     return 0;
  59. }
Success #stdin #stdout 0s 5512KB
comments (?)
stdin
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9
0 0 0 0 0 0 2 3 1
0 0 0 7 3 2 3 3 1
0 0 0 0 9 10 2 8 3
0 0 0 0 0 0 0 6 4
0 4 7 10 5 10 5 9 6
0 0 0 0 0 3 9 9 6
2 1 2 1 7 6 3 10 9
0 0 5 7 7 3 10 2 5
0 0 0 0 0 0 0 0 5
stdout
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0.000000
https://ideone.com/kWuiuG
language:
C (gcc 8.3)
created:
1 year ago
visibility:
public

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