RE: [Help-glpk] loop for mathprog

[Michael Hennebry]

On Wed, 15 Nov 2006, Robert Fourer wrote:

> How would what you want differ from the ability to write a script such as the
> one copied below?  It's a simple script for sensitivity analysis -- there are
> much more complicated examples -- but it serves as an example of how a 
> modeling
> language's own syntax could serve well as a scripting language.  Conversion
> between variable names and variable indices is not an issue here, because the
> user writes everything in terms of the symbolic model.

The difference is mostly in complexity.
Usually what I do is add a constraint that is a complex
function of the original problem and the current solution.
I might also run a heuristic to see if it
can find a new improved feasible solution.

When "printing", producing an intelligble
format is often problem-specific,
though it can often be approximated by leaving off zeros.
Often the "printed" result is just fodder for more computation.

> I have some sympathy for Andrew's view (see the copied message below), but
> maybe I see the tradeoff differently.  It's a tradeoff between having
> essentially the same language serving for both model definitions and script
> writing, and having a general-purpose programming language that works through
> an API to handle models written in a modeling language.  I have encountered
> optimization modelers on each side of this tradeoff.

I'd be happy with a documented mechanism for getting
and parsing a variable's name from its index number.
I could build my own symbol table.
It's been a release or two since I've used GLPK,
so for all I know, said mechanism might already be in place.

-- 
Mike   address@hidden
"it stands to reason that they weren't always called the ancients."
                                                      --  Daniel Jackson