Ising/IsingV1.c at master · bryanfoley/Ising · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
#include<float.h>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>


//Function Headers
int nmax=10;
void main(void);
void calculate(double spin[nmax][nmax],int nmax,double t,int n_passes,double current_mag,double current_energy,double ave_mag,double ave_energy);
void spin(void);
void init_spin(double spin[nmax][nmax],int nmax,double current_m,double current_e);
void initialise(double spin[nmax][nmax],int nmax,double t_init,double t_final,int n_points,int n_passes,double current_m,double current_e);
void test_for_edge(int x, int nmax);
void test_for_flip(double spin[nmax][nmax],int j,int k,double t,double sum,double current_mag,double current_energy);
double neighbours(double spin[nmax][nmax],int nmax,int j,int k);

//Declare Arrays


//main
void main(void)
{
 int i,j,k;

 double mag[nmax];
 double temp[nmax];
 double energy[nmax];
 double spin[nmax][nmax];

 double t;
 double dt;
 double t_init;
 double t_final;
 int n_points;
 int n_passes;
 double current_m;
 double current_e;
 double ave_mag;
 double ave_energy;
 double sum;


 initialise(spin,nmax,t_init,t_final,n_points,n_passes,current_m,current_e);
 dt = (t_final - t_init) / (n_points - 1);
 t = t_init;

 init_spin(spin,nmax,current_m,current_e);

 for(i = 0;i<n_points;i++)
 {
      calculate(spin,nmax,t,n_passes,current_m,current_e,ave_mag,ave_energy);
      temp[i]= t;
      t = t + dt;
 }
}

void initialise(double spin[nmax][nmax],int nmax,double t_init,double t_final,int n_points,int n_passes,double current_m,double current_e)
{
 t_init = 1;
 t_final = 5;
 n_points = 9;
 n_passes = 100;

 init_spin(spin,nmax,current_m,current_e);
}

void init_spin(double spin[nmax][nmax],int nmax,double current_m,double current_e)
{
 int i,j;
 for(i=0;i<nmax;i++)
   {
       for(j=0;j<nmax;j++)
          {
              spin[i][j] = 1;
          }
   }
   current_m = nmax*nmax;
   current_e = -2*(nmax*nmax);
}

void calculate(double spin[nmax][nmax],int nmax,double t,int n_passes,double current_mag,double current_energy,double ave_mag,double ave_energy)
{
     double sum;
     int i,j,k;
     double m_tmp = 0;
     double e_tmp = 0;
     int n = 0;
     double m[nmax];
     double e[nmax];
     int ts[nmax];

     m[0] = current_mag;
     e[0] = current_energy;
     ts[0] = 0;

     for(i = 0; i< n_passes;i++)
           {
                for(j = 0; j < nmax;j++)
                      {
                           for(k = 0;k<nmax;k++)
                                 {
                                    sum = neighbours(spin,nmax,j,k);
                                    test_for_flip(spin,j,k,t,sum,current_mag,current_energy);
                                 }
                      }
                      m[i+1] = current_mag;
                      e[i+1] = current_energy;
                      ts[i+1] = i;

                      if(i>(n_passes/2))
                         {
                            m_tmp = m_tmp + current_mag;
                            e_tmp = e_tmp + current_energy;
                            n = n+1;
                         }
           }
           ave_mag = m_tmp/n;
           ave_energy = e_tmp/n;
}

double neighbours(double spin[nmax][nmax],int nmax,int j,int k)
{
   double sum;
   int x1,y1,x2,y2,x3,y3,x4,y4;
   x1 = j;
   y1 = k + 1;
   test_for_edge(y1,nmax);
   x2 = j;
   y2 = k - 1;
   test_for_edge(y2,nmax);
   x3 = j + 1;
   y3 = k;
   test_for_edge(x3,nmax);
   x4 = j - 1;
   y4 = k;
   test_for_edge(x4,nmax);
   sum = spin[x1][y1] + spin[x2][y2] + spin[x3][y3] + spin[x4][y4];
   return(sum);
}

void test_for_edge(int x, int nmax)
{
   if( x < 1)
       x = nmax;
   if( x > nmax)
       x = 1;
}

void test_for_flip(double spin[nmax][nmax],int j,int k,double t,double sum,double current_mag,double current_energy)
{
 double denergy;

 denergy = 2 * (spin[j][k])*sum;
 if(denergy < 0)
    {
       spin[j][k] = - spin[j][k];
       current_mag = current_mag + 2*spin[j][k];
       current_energy = current_energy + denergy;
    }
    else if(exp(-denergy/t) > rand()/RAND_MAX)
       {
          spin[j][k] = -spin[j][k];
          current_mag = current_mag + 2 * spin[j][k];
          current_energy = current_energy + denergy;
       }
}