我有一个二维数组的一维数组表示：下面是一个6x6的例子：
[00000012300456700890100234500000] => [------]
[|0123|]
[|4567|]
[|8901|]
[|2345|]
[------]
典型尺寸为514 * 514个元素（512 + 2个晕圈单元）。我必须在四个处理器之间分配数据：
Rank 0: Rank 1: Rank 2: Rank 3:
[----] [----] [|456] [567|]
[|012] [123|] [|890] [901|]
[|456] [567|] [|234] [345|]
[|890] [901|] [----] [----]
也就是说，进入排名0的数据的最右边部分也必须转到要排名为1的数据的左侧部分，依此类推所有其他邻居对。
我知道如何制作大小为4x4的数据类型，但不知道如何将该数组的最后一个元素重新发送为另一个等级的新元素。
如何分发重叠数据？
=== EDIT ===
在使用Jonathon实施后......
我正在尝试使用char数组（2D）执行此操作，但是当从处理器/队列中收集它们时，我会收到“垃圾”。我改变了类型和所有内容，但无法弄清楚问题出在哪里。
void distributeBySend_c(unsigned char **global, const int globalrows, const int globalcols,
const int localrows, const int localcols,
const int rank, const int size,
MPI_Comm cartcomm, const int dims[2], const int coords[2]) {
MPI_Request reqs[dims[0]*dims[1]];
const int tag = 1;
if (rank == 0) {
MPI_Datatype block;
int starts[2] = {0,0};
int subsizes[2] = {localrows, localcols};
int sizes[2] = {globalrows, globalcols};
MPI_Type_create_subarray(2, sizes, subsizes, starts, MPI_ORDER_C, MPI_CHAR, &block);
MPI_Type_commit(&block);
int reqno=0;
for (int i=0; i<dims[0]; i++) {
int startrow = i*datasize;
int destcoords[2];
destcoords[0] = i;
for (int j=0; j<dims[1]; j++) {
int startcol = j*datasize;
destcoords[1] = j;
int dest;
MPI_Cart_rank(cartcomm, destcoords, &dest);
MPI_Isend(&(global[startrow][startcol]), 1, block, dest, tag, cartcomm, &reqs[reqno++]);
}
}
}
unsigned char **local = alloc2dImage(localrows, localcols);
MPI_Recv(&(local[0][0]), localrows*localcols, MPI_CHAR, 0, tag, cartcomm, MPI_STATUS_IGNORE);
if (rank == 0)
MPI_Waitall(dims[0]*dims[1], reqs, MPI_STATUS_IGNORE);
eachprintarr_c(local, localrows, localcols, rank, size);
}
我得到的结果是：
---
Rank 0: ? ? ? ?
Rank 0: � ' V �
Rank 0: � ' V �
Rank 0: � ' V �
---
Rank 1: ? ? ? ?
Rank 1: � � � %
Rank 1: � � � %
Rank 1: � � � %
---
Rank 2: ? + + +
Rank 2: � � � �
Rank 2: � � � �
Rank 2: � � � �
---
Rank 3: + + + ?
Rank 3: � � �
Rank 3: � � �
Rank 3: � � �
答案 0 :(得分：4)
不幸的是，您无法使用MPI_Scatterv执行此操作，因为发送的数据会重叠。
你最好的选择是用Sends / Recvs手动执行此操作，这很容易，但不能很好地扩展;或分散＆＃34;内部＆＃34;仅数据并让处理器执行典型的保护单元/光环交换以获得所需的重叠数据。两种方式编码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "mpi.h"
char **alloc2d(const int n, const int m);
void free2d(char **p);
void printarr(const char **const arr, const int n, const int m, const char *pref);
void eachprintarr(const char **const arr, const int n, const int m, const int myrank, const int size);
const int datasize = 2;
const int halosize = 1;
void distributeBySend(const char **const global, const int globalrows, const int globalcols,
const int localrows, const int localcols,
const int rank, const int size,
MPI_Comm cartcomm, const int dims[2], const int coords[2]) {
MPI_Request reqs[dims[0]*dims[1]];
const int tag = 1;
if (rank == 0) {
MPI_Datatype block;
int starts[2] = {0,0};
int subsizes[2] = {localrows, localcols};
int sizes[2] = {globalrows, globalcols};
MPI_Type_create_subarray(2, sizes, subsizes, starts, MPI_ORDER_C, MPI_CHAR, &block);
MPI_Type_commit(&block);
int reqno=0;
for (int i=0; i<dims[0]; i++) {
int startrow = i*datasize;
int destcoords[2];
destcoords[0] = i;
for (int j=0; j<dims[1]; j++) {
int startcol = j*datasize;
destcoords[1] = j;
int dest;
MPI_Cart_rank(cartcomm, destcoords, &dest);
MPI_Isend(&(global[startrow][startcol]), 1, block, dest, tag, cartcomm, &reqs[reqno++]);
}
}
}
char **local = alloc2d(localrows, localcols);
MPI_Recv(&(local[0][0]), localrows*localcols, MPI_CHAR, 0, tag, cartcomm, MPI_STATUS_IGNORE);
if (rank == 0)
MPI_Waitall(dims[0]*dims[1], reqs, MPI_STATUS_IGNORE);
eachprintarr((const char **const)local, localrows, localcols, rank, size);
}
void scatterAndExchange(const char **const global, const int globalrows, const int globalcols,
const int localrows, const int localcols,
const int rank, const int size,
MPI_Comm cartcomm, const int dims[2], const int coords[2]) {
const int lefttag=1, righttag=2, uptag=3, downtag=4;
char **local = alloc2d(localrows, localcols);
for (int i=0; i<localrows; i++)
for (int j=0; j<localcols; j++)
local[i][j] = '.';
MPI_Datatype tmp, globalblock;
MPI_Datatype localblock;
/* send just the interior data to the processors */
int starts[2] = {0,0};
int subsizes[2] = {datasize, datasize};
int sizes[2] = {globalrows, globalcols};
MPI_Type_create_subarray(2, sizes, subsizes, starts, MPI_ORDER_C, MPI_CHAR, &tmp);
MPI_Type_create_resized(tmp, 0, sizeof(char), &globalblock);
MPI_Type_commit(&globalblock);
starts[0] = halosize; starts[1] = halosize;
sizes[0] = localrows; sizes[1] = localcols;
MPI_Type_create_subarray(2, sizes, subsizes, starts, MPI_ORDER_C, MPI_CHAR, &localblock);
MPI_Type_commit(&localblock);
int displs[size];
int counts[size];
for (int dest=0; dest<size; dest++) {
int destcoords[2];
MPI_Cart_coords(cartcomm, dest, 2, destcoords);
int row = halosize + destcoords[0]*datasize;
int col = halosize + destcoords[1]*datasize;
counts[dest] = 1;
displs[dest] = col + row*globalcols;
}
const char *ptr = (rank == 0 ? &(global[0][0]) : NULL ) ;
MPI_Scatterv( ptr, counts, displs, globalblock,
&(local[0][0]), 1, localblock,
0, cartcomm);
/* now send overlap data to neighbors above and below */
int left, right, up, down;
MPI_Cart_shift(cartcomm, 1, 1, &left, &right);
MPI_Cart_shift(cartcomm, 0, 1, &down, &up);
MPI_Sendrecv(&(local[localrows-2*halosize][0]), halosize*localcols, MPI_CHAR, up, uptag,
&(local[0][0]), halosize*localcols, MPI_CHAR, down, uptag,
cartcomm, MPI_STATUS_IGNORE);
MPI_Sendrecv(&(local[halosize][0]), halosize*localcols, MPI_CHAR, down, downtag,
&(local[localrows-halosize][0]), halosize*localcols, MPI_CHAR, up, downtag,
cartcomm, MPI_STATUS_IGNORE);
/* now send overlap data to neighbors left and right */
MPI_Datatype column;
sizes[0] = localrows; sizes[1] = localcols;
subsizes[0] = localrows; subsizes[1] = halosize;
starts[0] = 0; starts[1] = 0;
MPI_Type_create_subarray(2, sizes, subsizes, starts, MPI_ORDER_C, MPI_CHAR, &column);
MPI_Type_commit(&column);
MPI_Sendrecv(&(local[0][localcols-2*halosize]), 1, column, right, righttag,
&(local[0][0]), 1, column, left, righttag,
cartcomm, MPI_STATUS_IGNORE);
MPI_Sendrecv(&(local[0][halosize]), 1, column, left, lefttag,
&(local[0][localcols-halosize]), 1, column, right, lefttag,
cartcomm, MPI_STATUS_IGNORE);
eachprintarr((const char **const)local, localrows, localcols, rank, size);
}
int main(int argc, char **argv) {
int rank, size;
int dims[2] = {0,0};
int coords[2];
int periods[2] = {0, 0};
const int reorder = 1;
MPI_Comm cartcomm;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Dims_create(size, 2, dims);
MPI_Cart_create(MPI_COMM_WORLD, 2, dims, periods, reorder, &cartcomm);
MPI_Comm_rank(cartcomm, &rank);
MPI_Cart_coords(cartcomm, rank, 2, coords);
int globalcols = datasize*dims[0]+2*halosize;
int globalrows = datasize*dims[0]+2*halosize;
int localcols = datasize+2*halosize;
int localrows = datasize+2*halosize;
char **global = NULL;
if (rank == 0) {
global = alloc2d(globalrows, globalcols);
for (int i=0; i<globalrows; i++)
for (int j=0; j<globalcols; j++)
global[i][j] = '.';
char val = 'a';
for (int i=halosize; i<globalrows-halosize; i++)
for (int j=halosize; j<globalcols-halosize; j++) {
global[i][j] = val;
val++;
if (val > 'z') val = 'a';
}
printf("Global array: ---\n");
printarr((const char ** const)global, globalrows, globalcols, "");
}
if (argv[1] && !strcmp(argv[1],"sendrecv")) {
if (rank == 0)
printf("---\nDistributing with Send/Recv:---\n");
distributeBySend((const char **const) global, globalrows, globalcols,
localrows, localcols,
rank, size,
cartcomm, dims, coords);
} else {
if (rank == 0)
printf("---\nDistributing with Scatter/exchange:---\n");
scatterAndExchange((const char **const)global, globalrows, globalcols,
localrows, localcols,
rank, size,
cartcomm, dims, coords);
}
MPI_Finalize();
return 0;
}
char **alloc2d(const int n, const int m) {
char *data = malloc( n*m * sizeof(int) );
char **ptrs = malloc( n*sizeof(int *) );
for (int i=0; i<n; i++)
ptrs[i] = &(data[i*m]);
return ptrs;
}
void free2d(char **p) {
free(p[0]);
free(p);
}
void printarr(const char **const arr, const int n, const int m, const char *pref) {
for (int i=0; i<n; i++) {
printf("%s", pref);
for (int j=0; j<m; j++) printf("%c", arr[i][j]);
printf("\n");
}
}
void eachprintarr(const char **const arr, const int n, const int m, const int myrank, const int size) {
char line[12];
sprintf(line, "Rank %3d: ", myrank);
for (int rank=0; rank<size; rank++) {
if (rank == myrank) {
printf("---\n");
printarr(arr, n, m, line);
}
MPI_Barrier(MPI_COMM_WORLD);
}
}
跑步给出
$ mpirun -np 4 ./scatter sendrecv
Global array: ---
......
.abcd.
.efgh.
.ijkl.
.mnop.
......
---
Distributing with Send/Recv:---
---
Rank 0: ....
Rank 0: .abc
Rank 0: .efg
Rank 0: .ijk
---
Rank 1: ....
Rank 1: bcd.
Rank 1: fgh.
Rank 1: jkl.
---
Rank 2: .efg
Rank 2: .ijk
Rank 2: .mno
Rank 2: ....
---
Rank 3: fgh.
Rank 3: jkl.
Rank 3: nop.
Rank 3: ....
$ mpirun -np 4 ./scatter scatter
Global array: ---
......
.abcd.
.efgh.
.ijkl.
.mnop.
......
---
Distributing with Scatter/exchange:---
---
Rank 0: ....
Rank 0: .abc
Rank 0: .efg
Rank 0: .ijk
---
Rank 1: ....
Rank 1: bcd.
Rank 1: fgh.
Rank 1: jkl.
---
Rank 2: .efg
Rank 2: .ijk
Rank 2: .mno
Rank 2: ....
---
Rank 3: fgh.
Rank 3: jkl.
Rank 3: nop.
Rank 3: ....