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GTAP Resources: Frequently Asked Question Details

Subject: Memory RAM for full RunGTAP

Question: I appreciate if anyone can give me hint regarding the amount of memory RAM we need to run the full RunGTAP. We're thinking in upgrading our computer systems and we have to consider the needs that models as RunGTAP and GTAPDyn impose. In particular we know that, for instance, the full RunGTAP model does not run in my PC with one giga memory -I get a message "unable to allocate sufficient memory. (I0STAT is 912)". Does anyone know how much memory is needed to run the full regional and sectoral specification model? In the case of GTAPDyn, how much is needed? Do you think it is advisable a more powerful computer like those with dou-processors? Are GEMPACK and RunGTAP compatible with UNIX? I have heard that is not feasible to expand the memory RAM further than 2 GB using the standard XP Professional, is that right? Overall, what do you advise: upgrade the memory RAM of the current PCs and run the models with UNIX or any upgrade WINDOWS or the acquisition of a type "server" system?

Answer: This is an interesting question and topic.

To run full GTAP (GTAP.TAB, comparative static, all regions and commodities) requires more than 2GB of RAM. To do the same for dynamic GTAP (GDYN.TAB) would require more memory. I say more about getting that much memory later.

However it may not be a good idea to try to solve the fully disaggregated versions of these models. GTAP provides excellent facilities for aggregating the models. Usually you can get just as good results for any specific policy question by making a suitable aggregation. And that will probably solve within 1 or 2GB of RAM, and solve much more quickly than the fully disaggregated model would. Trying to solve the fully disaggregated model is difficult because of memory problems and takes a very long time even if you have the memory etc.

Accessing more memory with GEMPACK
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> I have heard that is not feasible to expand the memory RAM further > than 2 GB using the standard XP Professional, is that right?
That is correct.

But recently there are Windows PCs with 64-bit processors and 64-bit XP operating system. These break the 2GB memory limit. In order to run GEMPACK on such a PC and access more than 2GB for each simulation, you need to install GEMPACK using a 64-bit Fortran compiler. We will support the Intel Fortran compiler (which runs on 32-bit and 64-bit PCs) with Release 10 of GEMPACK (due latish in 2007). We have a beta test version of Release 10 available to selected customers now.

You can read more about these issues in the paper "Running Simulations Faster on Multi-Processor or 64-Bit PCs via GEMPACK" by Mark Horridge and me. This paper is available at http://www.copsmodels.com/elecpapr/c15.htm

Dual processor machines
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These are now becoming commonly available for 32-bit and 64-bit PCs.
And Release 10 of GEMPACK provides a way of speeding up simulations on such machines - see the paper referred to above.
But that does not help with memory problems - indeed even more memory is need to sensibly make use of 2 or more processors. For example, if you want to use 2 processors to speed up a simulation and if that simulation needs 3GB of RAM, you will need that much memory for each processor (that is, total of 6GB).

Unix?
----
Yes, GEMPACK is available on Unix machines. But I would recommend going the 64-bit route (where your familiar other word-processing etc utilities are available).

Most importantly I would urge you and others to consider whether you can achieve your policy objectives by aggregating the model suitably. If so you can avoid the complications (and costs) of high memory PCs for the present - such machines will become mainstream soon but at present they are a bit at the cutting edge.


Source: E-mail Message

Date Added: 10/30/2006