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POMPI_Type_create_subarray and MPI_Gather
 

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    <p>I have to solve a little mpi problem. I have 4 slaves processes and each of these wants to send a 2d subarray (CHUNK_ROWS X CHUNK_COLUMNS) to master 0. Master 0 collects all chunks in ddd[ROWS][COLUMNS] and print it. I want to use MPI_Gather()</p> <pre><code>#include &lt;mpi.h&gt; #include &lt;iostream&gt; using namespace std; #define ROWS 10 #define COLUMNS 10 #define CHUNK_ROWS 5 #define CHUNK_COLUMNS 5 #define TAG 0 int** alloca_matrice(int righe, int colonne) { int** matrice=NULL; int i; matrice = (int **)malloc(righe * sizeof(int*)); if(matrice != NULL){ matrice[0] = (int *)malloc(righe*colonne*sizeof(int)); if(matrice[0]!=NULL) for(i=1; i&lt;righe; i++) matrice[i] = matrice[0]+i*colonne; else{ free(matrice); matrice = NULL; } } else{ matrice = NULL; } return matrice; } int main(int argc, char* argv[]) { int my_id, numprocs,length,i,j; int ndims, sizes[2],subsizes[2],starts[2]; int** DEBUG_CH=NULL; int** ddd=NULL; char name[BUFSIZ]; MPI_Datatype subarray=NULL; //MPI_Status status; MPI_Init(&amp;argc, &amp;argv) ; MPI_Comm_rank(MPI_COMM_WORLD, &amp;my_id) ; MPI_Comm_size(MPI_COMM_WORLD, &amp;numprocs) ; // Ottiene quanti processi sono attivi MPI_Get_processor_name(name, &amp;length); if(my_id!=0){ //creo una sottomatrice ripulita dalle ghost cells ndims=2; sizes[0] = CHUNK_ROWS+2; sizes[1] = CHUNK_COLUMNS+2; subsizes[0] = CHUNK_ROWS; subsizes[1] = CHUNK_COLUMNS; starts[0] = 1; starts[1] = 1; MPI_Type_create_subarray(ndims,sizes,subsizes,starts,MPI_ORDER_C,MPI_INT,&amp;subarray); MPI_Type_commit(&amp;subarray); DEBUG_CH = alloca_matrice(CHUNK_ROWS+2,CHUNK_COLUMNS+2); for(i=0; i&lt;CHUNK_ROWS+2; i++){ for(j=0; j&lt;CHUNK_COLUMNS+2; j++){ if(i==0 || i==CHUNK_ROWS+1 || j==0 || j==CHUNK_COLUMNS+1) DEBUG_CH[i][j] = 5; else DEBUG_CH[i][j] = 1; } } //MPI_Send(DEBUG_CH[0],1,subarray,0,TAG,MPI_COMM_WORLD); } if(my_id==0){ ddd = alloca_matrice(ROWS,COLUMNS); } MPI_Gather(DEBUG_CH[0],1,subarray,ddd[0],CHUNK_ROWS*CHUNK_COLUMNS,MPI_INT,0,MPI_COMM_WORLD); if(!my_id){ for(i=0; i&lt;ROWS; i++){ for(j=0; j&lt;COLUMNS; j++){ printf("%d ",ddd[i][j]); } printf("\n"); } } if(my_id) MPI_Type_free(&amp;subarray); MPI_Finalize(); // Chiusura di MPI. return 0; } </code></pre> <p>Thanks all.</p>
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