只阵宣布根进程 [英] Array declared only on root process

问题描述

在MPI使用Fortran具体而言，是有可能的，并且只有在根流程定义的一个不错的选择数组？例如这样的事情：

In MPI in Fortran specifically, is it possible and a good choice to have an array defined only on the root process? For example something like this:

program test
implicit none

include 'mpif.h'

all mpi_init(ierr)

call mpi_comm_rank(mpi_comm_world,myid,ierr)
call mpi_comm_size(mpi_comm_world,numproc,ierr) 

if (myid .eq. 0) then
    complex(8), dimension(:,:), allocatable :: array
end if

   ...

if (myid .eq. 0) then
    allocate(array(2,2))
end if

   ...

end program

正如您可以猜到，我已经尝试过这一点，这是行不通的，如Fortran的声明必须在最前面。但我希望解决的办法？

As you can guess, I already tried this and it does not work, as in Fortran declarations need to be on top. But I was hoping for a way around this?

这样的话，阵列还不会吃了我的虚拟内存吧？还是我误解的东西？

This way, the array would also not eat into my "virtual" memory right? Or am I misunderstanding something?

推荐答案

正如你指出，你不能在声明语句IF -blocks或之后的任何地方声明块的过程。不过，声明上的所有进程的数组 ALLOCATABLE ，并且仅适用于某些分配是允许的，在我看来一个不错的选择。

As you pointed out, you cannot have declaration statements in IF-blocks or anywhere after the declaration block of the procedure. However, declaring the array as ALLOCATABLE on all processes, and allocating only on some is allowed, and in my opinion a good choice.

! Declare as allocatable on all processes
complex(8), dimension(:,:), allocatable :: array

   ...

! Allocate only on some
if (myid .eq. 0) then
    allocate(array(2,2))
end if

这方式，程序将不会消耗上的其他进程的任何额外的内存。

This way, the program will not consume any additional memory on other processes.

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