John,

For something like the Erlang-B function the most robust way to handle it is to implement it as a GAMS extrinsic function. For more on extrinsic functions, check Appendix J of the GAMS User Guide or here:

http://www.gams.com/mccarl/mccarlhtml/e ... ctions.htm.

The short version is that this is a way to implement a complicated function with special handling for overflow cases, etc., in a programming language like C/C++/F90 and make this available to your GAMS code. Once you've got it programmed, the function can be used in a manner similar to the GAMS intrinsic functions like cos and sin and sigmoid. If you're used to programming and creating shared libraries, etc., then this shouldn't be a big deal, since we provide some examples with the GAMS system.

I've seen this request, or one much like it, before. In your case, are you treating the number of trunks as a variable or a constant in your model? I ask because it wouldn't be too hard to take a derivative wrt the volume of inbound calls, but doing so wrt the number of trunks seems to be a bigger challenge.

-Steve

On Mon, Apr 21, 2014 at 1:31 PM, John Ryan wrote:

What is the limitation in GAMS with respect to the largest number it can handle. I am looking at an ErlangB equation implementation where a subset of the formula is structured as [InboundCalls^number of trunks/Fact(number of trunks]. As the number of trunks increases I eventually receive an error message of "overflow in + operation (addop) and overflow in * operation (mulop)". It appears as the trunk number is increased to approximately 695, then the model is generating a number that is to large and you get the overflow error. I would appreciate any suggestions on how to expand the limitation on the upper bound or any other suggestions.

Thanks,

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