MPI_AllGather無法正確收集...所有元素的結果都是相同的值？

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

#define h 1 
#define XY0 0 
#define MAX_XY 5 
#define N 2 //particles per subdomain 
#define BLOCKS 4 
#define a 1 
#define b 1 

float velocityX(float x, float y); 
float velocityY(float x, float y); 
int malloc2dfloat(float ***array, int length); 

int main (int argc, char **argv) 
{ 
typedef struct { 
    float xcoord; 
    float ycoord; 
    float velx; 
    float vely; 
} particle; 

int points= (int) floor((MAX_XY - XY0)/h) + 1; 
int procsize = 2; 
int myid, nproc; 

MPI_Datatype particletype, oldtypes[1]; 
MPI_Aint offset[1], extent; 

MPI_Init(&argc, &argv); 
MPI_Comm_size(MPI_COMM_WORLD, &nproc); 
MPI_Comm_rank(MPI_COMM_WORLD, &myid); 
int startElementX, startElementY, endElementX, endElementY; 
particle* sub_pars = (particle*)malloc(sizeof(particle)*N); 

offset[0] = 0; 
int blockcounts[1]; 
blockcounts[0] = 4; 
oldtypes[0] = MPI_FLOAT; 
MPI_Type_struct(1, blockcounts, offset, oldtypes, &particletype); 
MPI_Type_commit(&particletype); 
particle* particles = (particle*)malloc(sizeof(particle) * N * procsize*procsize); 
if (nproc != procsize*procsize){ 
    printf("Must use np=4 -- split into 4 blocks"); 
    MPI_Abort(MPI_COMM_WORLD,1); 
} 

srand(time(NULL)+myid); 
if (myid == 0) 
{ 

    float mins[4]; 
    startElementX = 0; 
    startElementY = 0; 
    endElementX = (points/procsize)-1; 
    endElementY = (points/procsize) -1; 
} 
else if (myid == 1) 
{ 
    startElementX = 0; 
    startElementY = (points/procsize); 
    endElementX = (points/procsize) -1; 
    endElementY = points - 1; 
} 
else if (myid == 2) 
{ 
    startElementX = (points/procsize); 
    startElementY = 0; 
    endElementX = points - 1; 
    endElementY = (points/procsize) -1; 
} 
else 
{ 
    startElementX = (points/procsize); 
    startElementY = (points/procsize); 
    endElementX = points-1; 
    endElementY = points-1; 
} 


int i; 
float localmin; 
float mag; 
for (i=0; i<N; i++) 
{ 
    sub_pars[i].xcoord = ((startElementX + rand()/(RAND_MAX/(endElementX-startElementX+1)+1)))*h + XY0; 
    printf("%f\n", sub_pars[i].xcoord); 
    sub_pars[i].ycoord = ((startElementY + rand()/(RAND_MAX/(endElementY-startElementY+1)+1)))*h + XY0; 
    sub_pars[i].velx = velocityX(sub_pars[i].xcoord, sub_pars[i].ycoord); 
    sub_pars[i].vely = velocityY(sub_pars[i].xcoord, sub_pars[i].ycoord); 
    mag = sqrt(sub_pars[i].velx*sub_pars[i].velx + sub_pars[i].vely*sub_pars[i].vely); 
    if (i==0 || localmin > mag) localmin = mag; 
} 
printf("localmin of %d is %.2f \n", myid, localmin); 

MPI_Allgather(&sub_pars, 1, particletype, particles ,1, particletype, MPI_COMM_WORLD); 

MPI_Finalize(); 
if(myid == 0) 
{ 
int k; 
for (k=0; k<N*4; k++) 
{ 
    printf("test %.2f \n", particles[i].xcoord); 
} 
} 

return 0; 

} 
float velocityX(float x, float y) 
{ 
float temp = (a+(b*(y*y-x*x))/((x*x+y*y)*(x*x+y*y))); 
return temp; 
} 

float velocityY(float x, float y) 
{ 
float temp = (-1*(2*b*x*y)/((x*x+y*y)*(x*x+y*y))); 
return temp; 
}

它只是返回所有的粒子相同的值，但我知道他們正在每個線程內正確計算，那麼什麼是錯的我MPI_ALLGATHER，可有人請解釋應該怎麼看？MPI_AllGather無法正確收集...所有元素的結果都是相同的值？

來源

2013-10-04 HillaryD

如果您在收集時遇到問題，請首先嚐試一個更簡單的示例（例如，通過全部收集收集每個工人的ID）。我不認爲這裏的任何人想要通過所有的模擬邏輯來找出你的集合出錯的地方。 – us2012

您犯了一個非常常見的錯誤：您傳遞給MPI_Allgather的第一個參數中的&（address-of）運算符是不必要的。 sub_pars已經是一個指針，並調用MPI_Allgather與&sub_pars傳遞一個指針指向指針（位於main()例程的棧幀中的某個位置），而不是指向實際數據的指針。

來源

2013-10-12 16:29:22

MPI_AllGather無法正確收集...所有元素的結果都是相同的值？

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