并行计算之梯形积分

女爷i 2022-08-10 08:34 227阅读 0赞

方法1

#include<stdio.h>
    #include"mpi.h"
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len);
    double f(double x);
    
    int main(void)
    {
      int my_rank,comm_sz,n = 1024,local_n;
      double a = 0.0, b= 1.0 , h, local_a,local_b;
      double local_int,total_int;
      int source;
     
      MPI_Init(NULL,NULL);
      MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
      MPI_Comm_size(MPI_COMM_WORLD,&comm_sz);
      
      Get_input(my_rank, comm_sz, &a, &b, &n);
     
      h = (b-a)/n;
      local_n= n/comm_sz;
     
      local_a = a+my_rank * local_n * h;
      local_b = local_a + local_n * h;
      local_int = Trap(local_a ,local_b,local_n,h);
    
      if(my_rank!=0)		
      {
         MPI_Send(&local_int,1,MPI_DOUBLE,0,0,MPI_COMM_WORLD);
      }
      else
      {
         total_int = local_int;
    	 for(source =1; source <comm_sz; source++)
    	 {
    	    MPI_Recv(&local_int,1,MPI_DOUBLE,source,0,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
    		total_int += local_int;
    	 }
      }
      if(my_rank == 0)
      {
        printf("with n = %d trapezoids, our estimate\n",n);
    	printf("of the integral from %f to %f = %.15e\n",a,b,total_int);
      }
     
      MPI_Finalize();
      return 0;
    }
     
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len)
    {
      double estimate,i;
      int x;
      estimate = (f(left_endpt) + f(right_endpt))/2.0;
      for(i = 1; i <= trap_count-1 ; i++)
      {
        x = left_endpt + i*base_len;
    	estimate += f(x);
      }
      estimate = estimate*base_len;
      return estimate;
    }
     
    double f(double x)
    {
    	return 4/(1+x*x);
    }

VC6运行效果图

![20151115181717440][]

方法2（用到了MPI\_Reduce()函数）

#include<stdio.h>
    #include"mpi.h"
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len);
    double f(double x);
    int main(void)
    {
      int my_rank,comm_sz,n = 1024,local_n;
      double a = 0.0, b= 1.0 , h, local_a,local_b;
      double local_int,total_int;
      int source;
    
      MPI_Init(NULL,NULL);
      MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
      MPI_Comm_size(MPI_COMM_WORLD,&comm_sz);
    
      h = (b-a)/n;
      local_n= n/comm_sz;
    
      local_a = a+my_rank * local_n * h;
      local_b = local_a + local_n * h;
      local_int = Trap(local_a ,local_b,local_n,h);
      MPI_Reduce(&local_int, &total_int, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);<span style="white-space:pre">	</span>//2
      if(my_rank == 0)
      {
        printf("with n = %d trapezoids, our estimate\n",n);
    	printf("of the integral from %f to %f = %.15e\n",a,b,total_int);
      }
    
      MPI_Finalize();
      return 0;
    }
    
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len)
    {
      double estimate,i;
      int x;
      estimate = (f(left_endpt) + f(right_endpt))/2.0;
      for(i = 1; i <= trap_count-1 ; i++)
      {
        x = left_endpt + i*base_len;
    	estimate += f(x);
      }
      estimate = estimate*base_len;
      return estimate;
    }
    
    double f(double x)
    {
    	return 4/(1+x*x);
    }

VC6运行效果图

![20151115181717440][]

方法3（用到了MPI\_Bcast()函数进行广播）

#include<stdio.h>
    #include"mpi.h"
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len);
    double f(double x);
    void Get_input(			//3，用于输入数据
    	int my_rank,
    	int comm_sz,
    	double* a_p,
    	double* b_p,
    	double* n_p) {
    
    	if (my_rank==0) {
    		printf("Enter a, b, and n\n");
    		scanf("%lf %lf %d", a_p, b_p, n_p);
    	}
    	MPI_Bcast(a_p, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);
    	MPI_Bcast(b_p, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);
    	MPI_Bcast(n_p, 1, MPI_INT, 0, MPI_COMM_WORLD);
    }
    int main(void)
    {
      int my_rank,comm_sz,n = 1024,local_n;
      double a = 0.0, b= 1.0 , h, local_a,local_b;
      double local_int,total_int;
      int source;
    
      MPI_Init(NULL,NULL);
      MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
      MPI_Comm_size(MPI_COMM_WORLD,&comm_sz);
    
      Get_input(my_rank, comm_sz, &a, &b, &n);
    
      h = (b-a)/n;
      local_n= n/comm_sz;
    
      local_a = a+my_rank * local_n * h;
      local_b = local_a + local_n * h;
      local_int = Trap(local_a ,local_b,local_n,h);
      MPI_Reduce(&local_int, &total_int, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
      if(my_rank == 0)
      {
        printf("with n = %d trapezoids, our estimate\n",n);
    	printf("of the integral from %f to %f = %.15e\n",a,b,total_int);
      }
    
      MPI_Finalize();
      return 0;
    }
    
    double Trap(double left_endpt,double right_endpt,int trap_count,double base_len)
    {
      double estimate,i;
      int x;
      estimate = (f(left_endpt) + f(right_endpt))/2.0;
      for(i = 1; i <= trap_count-1 ; i++)
      {
        x = left_endpt + i*base_len;
    	estimate += f(x);
      }
      estimate = estimate*base_len;
      return estimate;
    }
    
    double f(double x)
    {
    	return 4/(1+x*x);
    }

VC6运行效果图

![Trap2_1.png][]

MPI运行效果图

![Trap2_2.png][]

[20151115181717440]: /images/20220731/97ae1fa12baf46d9af20ae9c2f34c83d.png
[Trap2_1.png]: http://218.196.43.18:8888/userfiles/Trap2_1.png
[Trap2_2.png]: http://218.196.43.18:8888/userfiles/Trap2_2.png