如何在Fortran中将指针分配给复杂的3D数组 [英] How to assign pointers to a complex 3d array in Fortran
问题描述
我想知道如何在Fortran中分配两个指针，一个指向复杂3d数组的实部，另一个指向同一数组的虚部.
I would like to know how to assign two pointers, one to the real part of a complex 3d array and another to the imaginary part of the same array in Fortran.
假设我已经这样定义了一个3d数组:
Let's say I have defined a 3d array as such:
复杂* 16，尺寸(:，:，:)，可分配，目标:: vftmp
complex*16, dimension(:,:,:), allocatable, target :: vftmp
，我想分配一个指向vftmp(2,1,1)实部的指针和一个指向vftmp(2,1,1)虚部的指针.有人可以帮我摘录吗?谢谢.
and I would like to assign a pointer to the real part of vftmp(2,1,1) and a pointer to the imaginary part of vftmp(2,1,1). Could someone help me with a snippet please? Thanks.
推荐答案
我希望以下内容是可能的
I hope something like the following is possible
real, pointer :: re
complex, target :: z
re => z % re
! or
real, pointer :: re(:,:,:)
complex, target :: z(2,3,4)
re => z(:,:,:) % re
，但似乎(或者对于非常新的编译器来说可能...?)所以下面是一种变通方法:
but it seems not (or possible with very new compilers...?) So a workaround approach below:
1)如果目标是获取复杂数组单个元素的Re和Im部分的(标量)指针，我想我们可以使用 c_f_pointer 这样
1) If the goal is to get (scalar) pointers for the Re and Im parts of a single element of a complex array, I guess we can use c_f_pointer such that
module testmod
contains
subroutine getreim_ptr( z, re, im )
use iso_c_binding
implicit none
complex, target, intent(in) :: z
real, pointer :: re, im, buf(:)
call c_f_pointer( c_loc( z ), buf, [ 2 ] )
re => buf( 1 )
im => buf( 2 )
end subroutine
end module
program main
use testmod
implicit none
complex :: z( 2, 3 )
real, pointer :: re, im
!! Test array.
z = 0.0
z( 1, 1 ) = ( 1.0, -1.0 )
!! Get pointers for the Re/Im parts of z(1,1).
call getreim_ptr( z( 1, 1 ), re, im )
print *, "z(1,:) = ", z(1,:)
print *, "z(2,:) = ", z(2,:)
print *, "re = ", re
print *, "im = ", im
end
结果(gfortran-8.2):
Result (gfortran-8.2):
z(1,:) = (1.00000000,-1.00000000) (0.00000000,0.00000000) (0.00000000,0.00000000)
z(2,:) = (0.00000000,0.00000000) (0.00000000,0.00000000) (0.00000000,0.00000000)
re = 1.00000000
im = -1.00000000
2)如果目标是获取整个复杂数组的数组指针，我想我们可以使用秩重映射指针分配(指向具有恒定间隙的非连续内存).例如，在2D情况下(为简单起见)，
2) If the goal is to get array pointers for the entire complex array, I guess we can use rank-remapping pointer assignments (to point to non-contiguous memory with constant gaps). For example, in the 2D case (for simplicity),
re( 1:n1, 1:n2 ) => buf( 1::2 )
im( 1:n1, 1:n2 ) => buf( 2::2 )
其中 re 和 im 是2D数组指针，而 buf 是真正的1D数组指针，它指向可分配的2D复杂数组(通过 c_f_pointer ).一个最小的例子可能是这样的:
where re and im are 2D array pointers and buf is a real 1D array pointer that points to an allocatable 2D complex array (via c_f_pointer). A minimum example may look like this:
module testmod
contains
subroutine getreim_ptr2d( zarr, re, im )
use iso_c_binding
implicit none
complex, allocatable, target, intent(in) :: zarr(:,:)
real, pointer :: re(:,:), im(:,:), buf(:)
integer :: n1, n2
n1 = size( zarr, 1 )
n2 = size( zarr, 2 )
call c_f_pointer( c_loc( zarr ), buf, [ size(zarr) * 2 ] )
re( 1:n1, 1:n2 ) => buf( 1::2 )
im( 1:n1, 1:n2 ) => buf( 2::2 )
end subroutine
end module
program main
use testmod
implicit none
complex, allocatable :: zarr(:,:)
real, pointer :: re(:,:), im(:,:)
integer i
!! Prepare a test array (zarr).
allocate( zarr( 2, 3 ) )
zarr(1,:) = [( complex( 100 + i, -100 -i ), i=1,3 )]
zarr(2,:) = [( complex( 200 + i, -200 -i ), i=1,3 )]
print *, "shape( zarr ) = ", shape( zarr )
print *, "zarr(1,:) = ", zarr(1,:)
print *, "zarr(2,:) = ", zarr(2,:)
call getreim_ptr2d( zarr, re, im )
print *
print *, "shape( re ) = ", shape( re )
print *, "re(1,:) = ", re(1,:)
print *, "re(2,:) = ", re(2,:)
print *
print *, "shape( im ) = ", shape( im )
print *, "im(1,:) = ", im(1,:)
print *, "im(2,:) = ", im(2,:)
end program
结果(gfortran 8.2):
Result (gfortran 8.2):
shape( zarr ) = 2 3
zarr(1,:) = (101.000000,-101.000000) (102.000000,-102.000000) (103.000000,-103.000000)
zarr(2,:) = (201.000000,-201.000000) (202.000000,-202.000000) (203.000000,-203.000000)
shape( re ) = 2 3
re(1,:) = 101.000000 102.000000 103.000000
re(2,:) = 201.000000 202.000000 203.000000
shape( im ) = 2 3
im(1,:) = -101.000000 -102.000000 -103.000000
im(2,:) = -201.000000 -202.000000 -203.000000
下面是一些我们可以在网上找到的材料:
Below are some materials we can find on the net:
Fortran 2003的新功能(N1597):3.7指针作业"
"......允许重排第一级数组的元素:
"...Remapping of the elements of a rank-one array is permitted:
p(1:m,1:2*m) => a(1:2*m*m)
映射按数组元素顺序进行，并且目标数组必须足够大.边界可以是任何标量整数表达式.排名第一的数组的限制是因为指针数组不需要占用连续的存储空间:
The mapping is in array-element order and the target array must be large enough. The bounds may be any scalar integer expressions. The limitation to rank-one arrays is because pointer arrays need not occupy contiguous storage:
a => b(1:10:2)
但在第一种情况下所有间隙的长度都相同."
but all the gaps have the same length in the rank-one case."
Fortran 2003扩展:5.4.3等级重映射指针分配(此页面)
"...此功能允许多维指针指向一维对象.例如:
"...This feature allows a multi-dimensional pointer to point to a single-dimensional object. For example:
REAL,POINTER :: diagonal(:),matrix(:,:),base(:)
...
ALLOCATE(base(n*n))
matrix(1:n,1:n) => base
diagonal => base(::n+1)
!
! DIAGONAL now points to the diagonal elements of MATRIX.
!
请注意，在进行排名重映射时，必须为所有维度明确指定上下限的值，没有默认值."
Note that when rank-remapping, the values for both the lower and upper bounds must be explicitly specified for all dimensions, there are no defaults."
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