Hi,
I have a problem with MPI_Senrecv communication where I send columns on
edges between processes.
For debugging, I show you below a basic example where I initialize a 10x10
matrix ("x0" array) with x_domain=4
and y_domain=4. For the test, I simply initialize the 2D array values with
x0[i][j] = i+j . After, in updateBound.c", I'm
using the MPI_Sendrecv functions for the North-South and Est-West process.
Here's the main program "example.c" :
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#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "mpi.h"
int main(int argc, char *argv[])
{
/* size of the discretization */
double** x;
double** x0;
int i,j,k,l;
int nproc;
int ndims;
int S=0, E=1, N=2, W=3;
int NeighBor[4];
int xcell, ycell, size_tot_x, size_tot_y;
int *xs,*ys,*xe,*ye;
int size_x = 4;
int size_y = 4;
int me;
int x_domains=2;
int y_domains=2;
MPI_Comm comm, comm2d;
int dims[2];
int periods[2];
int reorganisation = 0;
int row;
MPI_Datatype column_type;
size_tot_x=size_x+2*x_domains+2;
size_tot_y=size_y+2*y_domains+2;
xcell=(size_x/x_domains);
ycell=(size_y/y_domains);
MPI_Init(&argc, &argv);
comm = MPI_COMM_WORLD;
MPI_Comm_size(comm,&nproc);
MPI_Comm_rank(comm,&me);
x = malloc(size_tot_y*sizeof(double*));
x0 = malloc(size_tot_y*sizeof(double*));
for(j=0;j<=size_tot_y-1;j++) {
x[j] = malloc(size_tot_x*sizeof(double));
x0[j] = malloc(size_tot_x*sizeof(double));
}
xs = malloc(nproc*sizeof(int));
xe = malloc(nproc*sizeof(int));
ys = malloc(nproc*sizeof(int));
ye = malloc(nproc*sizeof(int));
/* Create 2D cartesian grid */
periods[0] = 0;
periods[1] = 0;
ndims = 2;
dims[0]=x_domains;
dims[1]=y_domains;
MPI_Cart_create(comm, ndims, dims, periods, reorganisation, &comm2d);
/* Identify neighbors */
NeighBor[0] = MPI_PROC_NULL;
NeighBor[1] = MPI_PROC_NULL;
NeighBor[2] = MPI_PROC_NULL;
NeighBor[3] = MPI_PROC_NULL;
/* Left/West and right/Est neigbors */
MPI_Cart_shift(comm2d,0,1,&NeighBor[W],&NeighBor[E]);
/* Bottom/South and Upper/North neigbors */
MPI_Cart_shift(comm2d,1,1,&NeighBor[S],&NeighBor[N]);
/* coordinates of current cell with me rank */
xcell=(size_x/x_domains);
ycell=(size_y/y_domains);
ys[me]=(y_domains-me%(y_domains)-1)*(ycell+2)+2;
ye[me]=ys[me]+ycell-1;
for(i=0;i<=y_domains-1;i++)
{xs[i]=2;}
for(i=0;i<=y_domains-1;i++)
{xe[i]=xs[i]+xcell-1;}
for(i=1;i<=(x_domains-1);i++)
{ for(j=0;j<=(y_domains-1);j++)
{
xs[i*y_domains+j]=xs[(i-1)*y_domains+j]+xcell+2;
xe[i*y_domains+j]=xs[i*y_domains+j]+xcell-1;
}
}
for(i=0;i<=size_tot_y-1;i++)
{ for(j=0;j<=size_tot_x-1;j++)
{ x0[i][j]= i+j;
// printf("%f\n",x0[i][j]);
}
}
/* Create column data type to communicate with South and North
neighbors */
MPI_Type_vector( ycell, 1, size_tot_x, MPI_DOUBLE, &column_type);
MPI_Type_commit(&column_type);
updateBound(x0, NeighBor, comm2d, column_type, me, xs, ys, xe, ye,
xcell);
for(i=0;i<=size_tot_y-1;i++)
{
free(x[i]);
free(x0[i]);
}
free(x);
free(x0);
free(xs);
free(xe);
free(ys);
free(ye);
MPI_Finalize();
return 0;
}
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and the second file "updateBound.c" which sends the columns and rows
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#include "mpi.h"
#include <stdio.h>
/*******************************************************************/
/* Update Bounds of subdomain with me process */
/*******************************************************************/
void updateBound(double** x,int NeighBor[], MPI_Comm comm2d, MPI_Datatype
column_type , int me, int* xs, int* ys, int* xe, int* ye, int xcell)
{
int S=0, E=1, N=2, W=3;
int flag;
MPI_Status status;
int i,j;
if(me==0) {printf("verif_update_before\n");
for(i=ys[me]-1;i<=ye[me]+1;i++)
{ for(j=xs[me]-1;j<=xe[me]+1;j++)
{ printf("%f ",x[i][j]);
}
printf("\n");
}
printf("\n");
}
/********* North/South communication **********************************/
flag = 1;
/*Send my boundary to North and receive from South*/
MPI_Sendrecv(&x[ys[me]][xs[me]], xcell, MPI_DOUBLE, NeighBor[N], flag,
&x[ye[me]+1][xs[me]], xcell, MPI_DOUBLE, NeighBor[S], flag, comm2d,
&status);
/*Send my boundary to South and receive from North*/
MPI_Sendrecv(&x[ye[me]][xs[me]], xcell, MPI_DOUBLE, NeighBor[S], flag,
&x[ys[me]-1][xs[me]], xcell, MPI_DOUBLE, NeighBor[N], flag, comm2d,
&status);
/********* Est/West communication ************************************/
flag = 2;
/*Send my boundary to Est and receive from West*/
MPI_Sendrecv(&x[ys[me]][xe[me]], 1, column_type, NeighBor[E], flag,
&x[ys[me]][xs[me]-1], 1, column_type, NeighBor[W], flag, comm2d, &status);
/*Send my boundary to West and receive from Est*/
MPI_Sendrecv(&x[ys[me]][xs[me]], 1, column_type, NeighBor[W], flag,
&x[ys[me]][xe[me]+1], 1, column_type, NeighBor[E], flag, comm2d, &status);
if(me==0) {printf("verif_update_after\n");
for(i=ys[me]-1;i<=ye[me]+1;i++)
{ for(j=xs[me]-1;j<=xe[me]+1;j++)
{ printf("%f ",x[i][j]);
}
printf("\n");
}
printf("\n");
}
}
------------------------------------------------------------------------------
Running with nproc=4, I print the values of the subarray with rank=0 (so at
left bottom of the grid) and I get before and after the
bounds udpate :
verif_update_before
6.000000 7.000000 8.000000 9.000000
7.000000 8.000000 9.000000 10.000000
8.000000 9.000000 10.000000 11.000000
9.000000 10.000000 11.000000 12.000000
verif_update_after
6.000000 5.000000 6.000000 9.000000
7.000000 8.000000 9.000000 12.000000
8.000000 9.000000 10.000000 *11.000000 *
9.000000 10.000000 11.000000 12.000000
As you can see, after the udpate, I don't have the correct value ( in
underligned bold : 11.0 ) at the second element
of the column coming from the Est. I expected 13.0 instead of 11.0.
So there's a problem with the column datatype which only send the first
element of this column.
In "example.c", I define the column as following :
MPI_Type_vector( ycell, 1, size_tot_x, MPI_DOUBLE, &column_type);
MPI_Type_commit(&column_type);
However, It seems ok and the computation of begin and end coordinates as a
function of rank "me" is also good.
I make you notice there's no problem between the exchange of rows between
the North and the South, only
between columns.
If you could help me, I don't know what to do.
Regards
