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jirina

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09-16-2019
03:57 AM

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"Passing" allocatable arrays of different sizes to module

I have several modules, each of them containing an allocatable array of a generally different size:

module Temperature real*4, allocatable, dimension(:,:,:) :: T end module Temperature module Pressure real*4, allocatable, dimension(:,:,:) :: p end module Pressure

I have another module that I would like to process allocatable arrays from the modules above, so I have

module ScalarOperations real*4, allocatable, dimension(:,:,:) :: scalar contains subroutine InitializeScalar ( ) scalar = 0.0 return end subroutine InitializeScalar end module ScalarOperations

I would like to do this:

module Temperature real*4, allocatable, dimension(:,:,:) :: T contains subroutine AllocateAndInitializeTemperature ( ) use ScalarOperations allocate ( T(10,20,30) ) scalar = T call InitializeScalar ( ) end subroutine AllocateAndInitializeTemperature end module Temperature

The source code line "scalar = T" is probably wrong and my question is what I should/can do to assign allocatable fields "T" and "p" to the allocatable array "scalar".

7 Replies

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Arjen_Markus

Valued Contributor II

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09-16-2019
04:11 AM

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Why not simply pass the array to the iniitialisation routine:

module ScalarOperations contains subroutine InitializeScalar ( scalar ) real*4, allocatable, dimension(:,:,:) :: scalar scalar = 0.0 return end subroutine InitializeScalar end module ScalarOperations

It is a lot clearer than using module variables - your intended solution would require pointer variables instead of allocatables.

(Side note: real*4 is not standard Fortran - better use real(kind=...), like real(kind=kind(1,0)) or the like)

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jirina

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09-16-2019
04:17 AM

27 Views

The main reason I wanted "scalar" to be a module variable is that there will be more subroutines in the module "ScalarOperations" working with the array "scalar". One option is thus pass the array to all subroutines working with it, another option is then pointer variables. I prefer the first option.

Thank you for your valuable answer and comments!

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FortranFan

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09-16-2019
08:01 AM

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jirina wrote:The main reason I wanted "scalar" to be a module variable is that there will be more subroutines in the module "ScalarOperations" working with the array "scalar". One option is thus pass the array to all subroutines working with it, another option is then pointer variables. I prefer the first option ..

Your original post and subsequent comment suggests you're interested in knowing the details with the semantics of MODULEs and module entities in Fortran (but if you think that's not the case, then you may want to reconsider what you know given instructions such as 'scalar = T' followed 'call AssignandIniitalizeScalar' in your code snippet which are questionable relative to any presumed intent). Toward this, the book Modern Fortran Explained is a better starting point to get a clean overview and your time will be better spent going through that book rather than reacting to tidbits on any peer forum such as this one: https://play.google.com/store/books/details/Modern_Fortran_Explained_Incorporating_Fortran_201?id=sB1rDwAAQBAJ&hl=en_US

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jimdempseyatthecove

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09-16-2019
09:06 AM

27 Views

Assuming from your description that given an arbitrary array (known external to the ScalarOperations) that you desire to have a series of procedures within ScalarOperations that operate on the same array: ProcedureFoo, ProcedureFi, ProcedureFo, ProcedureFum. Then consider using a contained procedure:

module Temperature real*4, allocatable :: T(:,:,:) end module Temperature module Pressure real*4, allocatable :: P(:,:,:) end module Pressure module ScalarOperations ! variables contains ! module procedures subroutine doScalarOperations(scalar) real*4 :: scalar(:,:,:) call ProcedureFee() call ProcedureFi() call ProcedureFo() call ProcedureFum contains ! subroutine contained procedures subroutine ProcedureFee scalar = scalar + 1.0 end subroutine ProcedureFee subroutine ProcedureFi scalar = scalar * 2.0 end subroutine ProcedureFi subroutine ProcedureFo scalar = scalar / 3.0 end subroutine ProcedureFo subroutine ProcedureFum scalar = sqrt(scalar) end subroutine ProcedureFum end subroutine doScalarOperations end module ScalarOperations program ProgScalarOperations use Temperature use Pressure use ScalarOperations implicit none allocate(T(10,20,30)) allocate(P(10,20,30)) call doScalarOperations(T) call doScalarOperations(P) end program ProgScalarOperations

Jim Dempsey

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jimdempseyatthecove

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09-16-2019
09:19 AM

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It should be noted that while it looks like you are saving the overhead of copying the (reference to the) array descriptor in the source code, the contained procedure call is doing this for you behind the scenes (for the used dummies from the outer scope).

This is a style matter.

Jim Dempsey

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jirina

Beginner

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09-16-2019
02:09 PM

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FortranFan wrote:Your original post and subsequent comment suggests you're interested in knowing the details with the semantics of MODULEs and module entities in Fortran (but if you think that's not the case, then you may want to reconsider what you know given instructions such as 'scalar = T' followed 'call AssignandIniitalizeScalar' in your code snippet which are questionable relative to any presumed intent). Toward this, the book Modern Fortran Explained is a better starting point to get a clean overview and your time will be better spent going through that book rather than reacting to tidbits on any peer forum such as this one: https://play.google.com/store/books/details/Modern_Fortran_Explained_Inc...

Thank you for recommending reading the book. I have it, I will read it and I will hopefully learn how to do what I need.

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FortranFan

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09-16-2019
07:59 PM

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jirina wrote:

Quote:

FortranFanwrote:

.. the book Modern Fortran Explained is a better starting point to get a clean overview and your time will be better spent going through that book rather than reacting to tidbits on any peer forum such as this one: https://play.google.com/store/books/details/Modern_Fortran_Explained_Inc...

Thank you for recommending reading the book. I have it, I will read it and I will hopefully learn how to do what I need.

That's really great. Once you've gone over it, you may want to review closely the sections on ELEMENTAL procedures, SELECT RANK facility, etc. Or better yet, you may want to look at your coding needs and consider whether you want to start with type safety (always IMPLICIT NONE), defined KINDs (see this, no *4 usage: https://software.intel.com/en-us/blogs/2017/03/27/doctor-fortran-in-it-takes-all-kinds), explicitly declared INTENTs in subprograms, and move on object-oriented code design even - a simple illustration of the code in your original post will be whether you meant like so, something you can try out with your Intel Fortran compiler:

module kinds_m implicit none integer, parameter :: R4 = selected_real_kind( p=6 ) integer, parameter :: R8 = selected_real_kind( p=12 ) end module module scalar_m use kinds_m, only : R4 implicit none type :: scalar_t real(kind=R4), allocatable :: vals(:,:,:) contains procedure, pass(this) :: Init => InitializeScalar ! Other methods to operate on scalars end type scalar_t contains subroutine InitializeScalar( this, val ) ! Argument list class(scalar_t), intent(inout) :: this real(R4), intent(in), optional :: val if ( present(val) ) then this%vals = val else this%vals = 0.0_r4 end if return end subroutine InitializeScalar end module scalar_m module Temperature_m use kinds_m, only : R4 use scalar_m, only : scalar_t implicit none type(scalar_t) :: T contains subroutine AllocateAndInitializeTemperature ( ) allocate ( T%vals(10,20,30) ) call T%Init( ) end subroutine AllocateAndInitializeTemperature end module Temperature_m module Pressure_m use kinds_m, only : R4 use scalar_m, only : scalar_t implicit none type(scalar_t) :: P contains subroutine AllocateAndInitializePressure( ) allocate ( P%vals(10,20,30) ) call P%Init( val=1.0_r4 ) end subroutine AllocateAndInitializePressure end module Pressure_m program test use Temperature_m, only : T, AllocateAndInitializeTemperature use Pressure_m, only : P, AllocateAndInitializePressure implicit none call AllocateAndInitializeTemperature() print *, T%vals(1,1,1) call AllocateAndInitializePressure() print *, P%vals(1,2,3) stop end program

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