我试图找到数组中所有给定数字的和。我必须把数组分成相等的大小，然后发送到每个进程并计算总和稍后，将每个进程计算出的和发回根进程以获得最终答案。实际上，我知道我可以使用MPI_Scatter但我的问题是如果我的单子是奇数怎么办。例如，我有一个带有13元素的数组，然后有3进程因此默认情况下，MPI_Scatter将数组除以3并保留最后一个元素基本上，它只计算12元素的和。我使用MPI_Scatter时的输出：
myid = 0 total = 6
myid = 1 total = 22
myid = 2 total = 38
results from all processors_= 66
size= 13
所以，我计划使用
MPI_Scatter和MPI_Send。所以我可以得到最后一个元素并通过MPI_Send发送它并计算它，然后在根进程中接收但我有问题我的代码：#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
/* globals */
int numnodes, myid, mpi_err;
int last_core;
int n;
int last_elements[];
#define mpi_root 0
/* end globals */
void init_it(int *argc, char ***argv);
void init_it(int *argc, char ***argv) {
mpi_err = MPI_Init(argc, argv);
mpi_err = MPI_Comm_size( MPI_COMM_WORLD, &numnodes );
mpi_err = MPI_Comm_rank(MPI_COMM_WORLD, &myid);
}
int main(int argc, char *argv[]) {
int *myray, *send_ray, *back_ray;
int count;
int size, mysize, i, k, j, total;
MPI_Status status;
init_it(&argc, &argv);
/* each processor will get count elements from the root */
count = 4;
myray = (int*)malloc(count * sizeof(int));
size = (count * numnodes) + 1;
send_ray = (int*)malloc(size * sizeof(int));
back_ray = (int*)malloc(numnodes * sizeof(int));
last_core = numnodes - 1;
/* create the data to be sent on the root */
if(myid == mpi_root){
for(i = 0; i < size; i++)
{
send_ray[i] = i;
}
}
/* send different data to each processor */
mpi_err = MPI_Scatter( send_ray, count, MPI_INT,
myray, count, MPI_INT,
mpi_root, MPI_COMM_WORLD);
if(myid == mpi_root) {
n = 1;
memcpy(last_elements, &send_ray[size-n], n * sizeof(int));
//Send the last numbers to the last core through send command
MPI_Send(last_elements, n, MPI_INT, last_core, 99, MPI_COMM_WORLD);
}
/* each processor does a local sum */
total = 0;
for(i = 0; i < count; i++)
total = total + myray[i];
//total = total + send_ray[size-1];
printf("myid= %d total= %d\n", myid, total);
if(myid == last_core)
{
printf("Last core\n");
MPI_Recv(last_elements, n, MPI_INT, 0, 99, MPI_COMM_WORLD, &status);
}
/* send the local sums back to the root */
mpi_err = MPI_Gather(&total, 1, MPI_INT,
back_ray, 1, MPI_INT,
mpi_root, MPI_COMM_WORLD);
/* the root prints the global sum */
if(myid == mpi_root){
total=0;
for(i = 0; i < numnodes; i++)
total = total + back_ray[i];
printf("results from all processors_= %d \n", total);
printf("size= %d \n ", size);
}
mpi_err = MPI_Finalize();
}
输出：
myid = 0 total = 6
myid = 1 total = 22
myid = 2 total = 38
Last core
[ubuntu:11884] *** An error occurred in MPI_Recv
[ubuntu:11884] *** on communicator MPI_COMM_WORLD
[ubuntu:11884] *** MPI_ERR_TRUNCATE: message truncated
[ubuntu:11884] *** MPI_ERRORS_ARE_FATAL: your MPI job will now abort
--------------------------------------------------------------------------
mpiexec has exited due to process rank 2 with PID 11884 on
node ubuntu exiting improperly. There are two reasons this could occur:
1. this process did not call "init" before exiting, but others in
the job did. This can cause a job to hang indefinitely while it waits
for all processes to call "init". By rule, if one process calls "init",
then ALL processes must call "init" prior to termination.
2. this process called "init", but exited without calling "finalize".
By rule, all processes that call "init" MUST call "finalize" prior to
exiting or it will be considered an "abnormal termination"
This may have caused other processes in the application to be
terminated by signals sent by mpiexec (as reported here).
我知道我做错了。如果你能指点我，我将不胜感激。
最佳答案
上一个元素数组没有指定大小MPI_Recv错误，因为没有空间放置正在发送的项目。您的代码缺少最后一个元素的malloc。
关于c - 如何在C中使用MPI查找给定数字的总和？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/19239111/