integral1_mpi.c 3.02 KB
Newer Older
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
// calculate integral using master-workers model
// compile:  mpicc integral1_mpi.c -lm
// usage: mpirun -n process# ./a.out trial#

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <limits.h>
#include <mpi.h>


// w is gaussian weight function
double w(double x, double y)
{
  return exp( - ( x*x + y*y ) );
}



void generator(double * x, double * y)
{
   double xt, yt, ratio, tmp ;
   double delta = 0.5 ;


   tmp = (double)rand() / (double)RAND_MAX  ;
// update x by adding a multiples of delta , (2 * tmp - 1) creates a number between -1.0 and 1.0
   xt = (*x) + delta * (2 * tmp - 1) ; 

   tmp = (double)rand() / (double)RAND_MAX  ;
// update y by adding a multiples of delta , (2 * tmp - 1) creates a number between -1.0 and 1.0
   yt = (*y) + delta * (2 * tmp - 1) ; 


// compare updated x,y values with old x,y values, accept or reject updated values as new values according to weight function
   ratio = w(xt, yt ) / w(*x, *y) ;
   tmp = (double)rand() / (double)RAND_MAX  ;

   if(ratio > tmp )
   {

      *x = xt ;
      *y = yt ;
   }


}


//f is the function to be integrated
double f(double x, double y)
{


return M_PI *  ( x*x + y*y ) ;

}


int main(int argc, char* argv[])
{
   double  x, y ;
   double * x_array ;
   double * y_array ;

   double sum ;
   double total_sum ;
   double integral ;
   int trials, trials_per_p;
   int i, j ;
   int pnumber, myrank;

   MPI_Status status;
   MPI_Init(&argc,&argv);
   MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
   MPI_Comm_size(MPI_COMM_WORLD, &pnumber);




   x = 0.0 ;
   y = 0.0 ;


   trials = atoi(argv[1]);
   trials_per_p = trials / (pnumber - 1 );

   x_array = malloc( trials_per_p * sizeof(double)) ;
   y_array = malloc( trials_per_p * sizeof(double)) ;



   if(myrank == 0) //master process generates random numbers and sends them to workers
   {
      for(j=1 ; j < pnumber ; j++)
      {
         for(i=0 ; i < trials_per_p ; i++)
         {
            generator(&x, &y);
               x_array[i] = x ;
               y_array[i] = y ;
         }

         MPI_Send(x_array, trials_per_p , MPI_DOUBLE, j, 1234 , MPI_COMM_WORLD) ; 
         MPI_Send(y_array, trials_per_p , MPI_DOUBLE, j, 5678 , MPI_COMM_WORLD) ;    

      }
   }


   if(myrank != 0) // worker processes receive random numbers from master process and calculate sum
   {

      MPI_Recv(x_array, trials_per_p, MPI_DOUBLE, 0, 1234, MPI_COMM_WORLD, &status) ;
      MPI_Recv(y_array, trials_per_p, MPI_DOUBLE, 0, 5678, MPI_COMM_WORLD, &status) ;

      sum = 0.0 ;
      for(i=0 ; i < trials_per_p ; i++)
      {

         sum += f(x_array[i], y_array[i]) ;
      } 


   }

   MPI_Reduce(&sum, &total_sum, 1, MPI_DOUBLE , MPI_SUM, 0, MPI_COMM_WORLD) ; // all calculated sums are accumulated in master process

   
   if(myrank == 0)
   {
      integral = total_sum / ( (pnumber -1) * trials_per_p ) ;
      printf("%f %f\n", integral , M_PI);
   }


   MPI_Finalize();

   return 0;

}