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  1. #include <stdio.h>
  2. #define N 3
  3.  
  4. int main(void) {
  5.     int i, j, k;
  6.     double a[N][N] = {
  7.         { 0,1,-3 },
  8.         { 1,2,4 },
  9.         { 2,1,-1 },
  10.         { -11,13,5 }
  11.     };
  12.     double b[N] = { 18, 21, 5, 16 }, s;
  13.  
  14.     // 行列と定数項の出力
  15.     for (i = 0; i < N; i++) {
  16.         for (j = 0; j < N; j++) {
  17.             printf("%5.2lf ", a[i][j]);
  18.         }
  19.         printf(" | %5.2lf\n", b[i]);
  20.     }
  21.     printf("-------------------------------\n");
  22.  
  23.     // 前進消去
  24.     for (k = 0; k < N - 1; k++) {
  25.         for (i = k + 1; i < N; i++) {
  26.             double factor = a[i][k] / a[k][k];
  27.             for (j = k; j < N; j++) {
  28.                 a[i][j] -= factor * a[k][j];
  29.             }
  30.             b[i] -= factor * b[k];
  31.         }
  32.     }
  33.  
  34.     // 後退代入
  35.     double x[N];
  36.     for (i = N - 1; i >= 0; i--) {
  37.         s = b[i];
  38.         for (j = i + 1; j < N; j++) {
  39.             s -= a[i][j] * x[j];
  40.         }
  41.         x[i] = s / a[i][i];
  42.     }
  43.  
  44.     // 結果出力
  45.     for (k = 0; k < N; k++) {
  46.         printf("x[%d] = %5.2lf\n", k, x[k]);
  47.     }
  48.  
  49.     return 0;
  50. }
Success #stdin #stdout 0s 5304KB
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stdin
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Standard input is empty
stdout
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 0.00  1.00 -3.00  | 18.00
 1.00  2.00  4.00  | 21.00
 2.00  1.00 -1.00  |  5.00
-------------------------------
x[0] =  -nan
x[1] =  -nan
x[2] =  -nan
https://ideone.com/cukFe8
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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