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  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. void gauss3(double A[3][3], double b[3], double x[3]) {
  5. for (int i = 0; i < 3; i++) {
  6. // Normalize pivot row
  7. double pivot = A[i][i];
  8. for (int j = 0; j < 3; j++) A[i][j] /= pivot;
  9. b[i] /= pivot;
  10.  
  11. // Eliminate other rows
  12. for (int k = 0; k < 3; k++) {
  13. if (k == i) continue;
  14. double factor = A[k][i];
  15. for (int j = 0; j < 3; j++) A[k][j] -= factor * A[i][j];
  16. b[k] -= factor * b[i];
  17. }
  18. }
  19.  
  20. for (int i = 0; i < 3; i++) x[i] = b[i];
  21. }
  22.  
  23. int main() {
  24. double xval[8] = {0.15708, 0.23982, 0.37400, 0.57120, 0.82674, 1.04720, 1.23200, 1.43452};
  25. double yval[8] = {0.98769, 0.97138, 0.93087, 0.84125, 0.67728, 0.50000, 0.33236, 0.13586};
  26.  
  27. double S2=0, S4=0, S6=0, S8=0;
  28. double Sy=0, S2y=0, S4y=0;
  29.  
  30. for (int i = 0; i < 8; i++) {
  31. double x2 = xval[i] * xval[i];
  32. double x4 = x2 * x2;
  33. double x6 = x4 * x2;
  34. double x8 = x4 * x4;
  35.  
  36. S2 += x2;
  37. S4 += x4;
  38. S6 += x6;
  39. S8 += x8;
  40.  
  41. Sy += yval[i];
  42. S2y += x2 * yval[i];
  43. S4y += x4 * yval[i];
  44. }
  45.  
  46. double A[3][3] = {
  47. {8, S2, S4},
  48. {S2, S4, S6},
  49. {S4, S6, S8}
  50. };
  51.  
  52. double b[3] = {Sy, S2y, S4y};
  53. double sol[3];
  54.  
  55. gauss3(A, b, sol);
  56.  
  57. printf("Model 2 coefficients:\n");
  58. printf("b1 = %.6f\n", sol[0]);
  59. printf("b2 = %.6f\n", sol[1]);
  60. printf("b3 = %.6f\n", sol[2]);
  61.  
  62. double E = 0;
  63. for (int i = 0; i < 8; i++) {
  64. double x2 = xval[i] * xval[i];
  65. double x4 = x2 * x2;
  66. double yhat = sol[0] + sol[1]*x2 + sol[2]*x4;
  67. double diff = yval[i] - yhat;
  68. E += diff * diff;
  69. }
  70.  
  71. printf("Squared error E = %.10f\n", E);
  72.  
  73. printf("\nModel 2 predicted values:\n");
  74. for (int i = 0; i < 8; i++) {
  75. double x2 = xval[i] * xval[i];
  76. double x4 = x2 * x2;
  77. double yhat = sol[0] + sol[1] * x2 + sol[2] * x4;
  78. printf("%f\n", yhat);
  79. }
  80.  
  81. return 0;
  82. }
  83.  
Success #stdin #stdout 0s 5316KB
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stdin
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Standard input is empty
stdout
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Model 2 coefficients:
b1 = 0.999699
b2 = -0.496930
b3 = 0.037543
Squared error E = 0.0000005016

Model 2 predicted values:
0.987460
0.971243
0.930925
0.841562
0.677587
0.499900
0.331937
0.136076
https://ideone.com/yazl1i
language:
C (gcc 8.3)
created:
16 hours ago
visibility:
public

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