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From: Craig Rasmussen (crasmussen_at_[hidden])
Date: 2005-12-07 11:56:29


Begin forwarded message:

> From: Malcolm Cohen <malcolm_at_[hidden]>
> Date: November 21, 2005 11:23:59 AM MST
> To: Aleksandar Donev <adonev_at_[hidden]>
> Cc: J3 <j3_at_[hidden]>
> Subject: (j3.2005) Re: Derived types according to MPI2
>
> Aleksandar Donev said:
>> Yes, but the interesting thing is neither me nor Van were aware of
>> what
>> the standard actually allows in terms of derived types and the
>> storage
>> for the components, and presumably we know Fortran better. Can
>> storage
>
> One might have hoped so.
>
>> for the components be separated from the scalar derived type itself?
>
> Hey, when *I* am the Fortran processor there's no contiguous storage,
> or for that matter addressable storage! Don't take too limited a view
> of current "hard" ware.
>
>> how something is done as long as it is done well. But if you want to
>> pass an array of derived types to a parallel IO routine that is not
>> compiled by your super-smart Fortran compiler that chooses to scatter
>> the components across virtual-address space (yes, I mean virtual),
>> then
>> you do NOT want that abstraction.
>
> You cannot be serious. You do realise that there is no requirement on
> any array even on intrinsic data types to contain the "actual data".
> Is that a problem in practice? No of course not.
>
> The Fortran standard doesn't mention virtual addressing, physical
> addressing or any of these things. Is that a problem? No.
>
> What the standard should do (and usually does) is to specify the
> behaviour
> of the Fortran "virtual machine", i.e. the meaning of the program.
> How
> that program gets mapped to hardware is way outside the scope of the
> standard.
>
>> It is about choice. Leave preaching to the preachers. Programming
>> is a
>> profession for a reason---programmers are experienced and educated
>> and
>> understand the issues and don't need lectures on abstractions.
>
> Apparently not.
>
> Cheers,
> --
> ...........................Malcolm Cohen, NAG Ltd., Oxford, U.K.
> (malcolm_at_[hidden])
>
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