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  1. #include<iostream>
  2. #include<cmath>
  3. #include<fstream>
  4.  
  5. double U_K(double K,double a,double u);
  6.  
  7. using namespace std;
  8. int main()
  9. {
  10. 	cout<<"Enter set of possible lattice vector's i.e., 'N' & 'U'\t:\t"<<endl;
  11. 	int N ; double u ;
  12. 	cin>>N>>u;
  13. 	double a = 1;
  14. 	double K[2*N+1];
  15.  
  16. 	int j=0;
  17. 	//assigning value to 'K' i.e., lattice vectors (-N to N)
  18. 	for(int i = -N; i <=N ; i++)
  19. 	{
  20. 		K[j] = (2*3.14*i)/a;
  21. 		j++;
  22. 	}
  23.  
  24. 	int r = 2*N+1, c = 2*N+1;
  25. 	double mat[r][c],k=0;
  26.  
  27. 	ofstream ofs("data_cmp_U-2_N_3.txt");
  28. 	//varying wave-vector i.e., "k"
  29. 	for(double k = (-3.14)/a ; k < (3.14/a) ; k += 0.1)
  30. 	{
  31. 		for(int i=0; i < r ; i++)
  32. 		{
  33. 			for(int j=0; j < c ; j++)
  34. 			{
  35. 				if (i == j) mat[i][j] = (0.5)*pow((k - K[i]),2);
  36. 				else mat[i][j] = U_K(K[j] - K[i],a,u);
  37. 			}
  38. 		}
  39.  
  40. 		double ftr;
  41. 		//digonalizing matrix to find energy eigen-values
  42. 		for(int i=0;i<r;i++)
  43. 		{
  44. 			ftr =0;
  45. 			for(int j=0 ; j<c ;j++)
  46. 			{
  47. 				if(i>j)
  48. 				{
  49. 					ftr = mat[i][j]/mat[j][j];
  50. 					for( int k=0; k<c;k++)
  51. 					{
  52. 						mat[i][k] -= ftr*mat[j][k];
  53. 					}
  54. 				}
  55.  
  56. 			}
  57. 		}
  58.  
  59. 		for(int i=r-1;i>=0;i--)
  60. 		{	
  61. 			ftr =0;
  62. 			for(int j=c-1 ; j>=0 ;j--)
  63. 			{
  64. 				if(i<j) 
  65. 				{
  66. 					ftr = mat[i][j]/mat[j][j];
  67. 					for( int k=0; k<c;k++)
  68. 					{
  69. 						mat[i][k] -= ftr*mat[j][k];
  70. 					}
  71. 				}
  72. 			}
  73.  
  74. 		}
  75. 		ofs<<k<<"\t\t";
  76. 		for(int i =0 ; i< r;i++)
  77. 		{
  78. 			for(int j =0 ; j < c ; j++)
  79. 			{	
  80. 				if(i == j) ofs<<mat[i][j]<<"\t\t";
  81. 			}	
  82. 		}
  83. 		ofs<<endl;		
  84. 	}
  85.  
  86.  
  87. 	return 0;
  88. }
  89.  
  90. double U_K(double K,double a,double u)
  91. {
  92. 	return u*exp(-K)/a;
  93. }
Success #stdin #stdout 0.01s 5304KB
comments (?)
stdin 
Standard input is empty
stdout 
Enter set of possible lattice vector's i.e., 'N' & 'U'	:
https://ideone.com/X51rqD
language:
C++ (gcc 8.3)
created:
15 days ago
visibility:
public

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