nested ALLOCATABLEs

Hi!

I have an allocation problem: my memory is too small for my variables.
To solve this I seek help!
Background: an atmospheric dispersion model that makes concentration
maps of a set of dispersed substances.

I have a module that supports variables of type SubstanceVector, an
array with a fixed length:

MaxNSubstances = 242

TYPE SubstanceVector
REAL(Float), DIMENSION(MaxNSubstances) :: Values
END TYPE SubstanceVector

There is a database providing all characteristics for the 242
substances. The module contains operators, functions etcetera for all
sorts of transformations and reactions of the substances. In practice,
a regular problem uses about 30 different substances, but you never
know which ones on beforehand. Based on the input parameters, the
first step in my program is to find out the final subset of substances
for this problem.

Another module supports maps. To get a map of the relevant substances,
there is a user-defined type:

TYPE SampleGridType
.......
TYPE(SubstanceVector), DIMENSION(:,:,, ALLOCATABLE ::
Concentration
.......
END TYPE SampleGridType

With 242 substances and a map of 151 * 91 grid nodes for
concentrations at 5 vertical levels, the space to be allocated for
just the concentration component becomes about 67 MB when 4-byte reals
are used. My pc has just 504 MB and "concentration" is not the only
component of SampleGridType.

To reduce memory needed for allocation, I would like to be able to set
the value of MaxNSubstances at runtime once I know which subset will
be used. Or have the "Values" component of SubstanceVector
allocatable. But then an attempt to allocate space for SampleGridType
%Concentration will fail.

I could glue the two datatypes together and have something like

TYPE SampleGridType
REAL(Float), DIMENSION(:,:,:,, ALLOCATABLE :: Concentration
END TYPE SampleGridType

where the first and fastest running index now refers to the number of
the substance. Now all my nice operators and functions from the
substance module are useless, since SubstanceVector does not make
sense anymore.

--> Which combination of user-defined types, alternative to the above
SubstanceVector and SampleGridType, will facilitate the construction
of maps of a VARIABLE collection of substances?

Regards,


Arjan

Arjan <arjan.van.dijk@rivm.nl> wrote:

> TYPE SubstanceVector
> REAL(Float), DIMENSION(MaxNSubstances) :: Values
> END TYPE SubstanceVector
....
> TYPE SampleGridType
> ......
> TYPE(SubstanceVector), DIMENSION(:,:,, ALLOCATABLE ::
> Concentration
> ......
> END TYPE SampleGridType
....
> To reduce memory needed for allocation, I would like to be able to set
> the value of MaxNSubstances at runtime once I know which subset will
> be used. Or have the "Values" component of SubstanceVector
> allocatable. But then an attempt to allocate space for SampleGridType
> %Concentration will fail.

I don't see why... other than that you have to allocate an object
instead of a type, but that has little to do with anything you
mentioned, so I assume that is just a slip of the keyboard... or maybe
not.

When you say that the allocation "will fail" do you mean that you
actually tried it and it failed, or that you think it would fail? If you
actually tried it and it failed, I'd like to see the exact code and
error message. If you just think it will fail, I think you are wrong.

You will have to make values allocatable, as you imply.

The only thing worthy of note here is that, if samplegrid is a variable
of type samplegridtype, you will need to allocate each
samplegrid%concentration(i)%values to the desired size. You do have to
allocate separately for each i, because each i has a separate
allocatable component. So just do it in a loop. If you are trying to do
it in a single allocation, that might be your problem. Otherwise, I
think you'll have to show exactly what this you are doing that is
failing, as it isn't evident from the description.

--
Richard Maine | Good judgement comes from experience;
email: last name at domain . net | experience comes from bad judgement.
domain: summertriangle | -- Mark Twain