Re: Adding if/then/else statement to GMPL

Hello !

I just finished adding the parsing code to parse this dummy model:

https://github.com/mingodad/GLPK/blob/local-set-param/examples/cut2.mod

On that branch I've added let/repeat/problem and relaxed the only one 
solve requirement, only the parsing is done (although corner cases can 
be missing).

Any comment/suggestion/help is welcome !

=====

./glpsol --genonly  -m cut2.mod
 >./glpsol --genonly  -m cut2.mod
GLPSOL: GLPK LP/MIP Solver, v4.65
Parameter(s) specified in the command line:
  --genonly -m cut2.mod
Reading model section from cut2.mod...
Reading data section from cut2.mod...
135 lines were read
Checking (line 14)...
Generating Number...
Generating Fill...
Generating Reduced_Cost...
Generating Width_Limit...
Display statement at line 46
problem Cutting_Opt: Cut, Number, Fill;
problem Pattern_Gen: Use, Reduced_Cost, Width_Limit;
problem Mix: Cut, Reduced_Cost;
Display statement at line 58
price[20] = 0.166667
price[45] = 0.416667
price[50] = 0.5
price[55] = 0.5
price[75] = 0.833333
Model has been successfully generated
 >Exit code: 0

=====

Cheer !

On 24/8/20 17:02, Meketon, Marc wrote:
> Since GMPL is a subset of AMPL, I would begin by looking at:
> https://ampl.com/BOOK/CHAPTERS/16-script.pdf
>
> As far as examples, the classic 'cutting stock' problem is a good one.  The AMPL site has two different iterative approaches:
> https://ampl.com/BOOK/EXAMPLES/EXAMPLES2/cut.mod
>
> https://ampl.com/BOOK/EXAMPLES/EXAMPLES2/cut.run
>
> and
>
> https://ampl.com/BOOK/EXAMPLES/EXAMPLES2/cut2.mod
>
> https://ampl.com/BOOK/EXAMPLES/EXAMPLES2/cut2.run
>
> and the data file is at:
> https://ampl.com/BOOK/EXAMPLES/EXAMPLES2/cut.dat
>
>
> -----Original Message-----
> From: Domingo Alvarez Duarte <[email protected]>
> Sent: Monday, August 24, 2020 10:34 AM
> To: Meketon, Marc <[email protected]>; Andrew Makhorin <[email protected]>; [email protected]
> Subject: Re: Adding if/then/else statement to GMPL
>
> Hello Meketon !
>
> Could you share your view of how it would be expressed (an ideal model
> sample) ?
>
> If you want to talk about it, maybe I'll be interested in implement it !
>
> Can you share a collection of models data to be used as base for the test/implementation ?
>
> Cheers !
>
> On 24/8/20 16:00, Meketon, Marc wrote:
>> I've always felt that GMPL needed if-then-else, for-loops, 'let' statements and the ability to re-solve to be a true modeling language.  And Andrew has always disagreed.
>>
>> Many of the models that I create ultimately are 'iterative' where I need to take the results of one model and use it to setup another model.  To me, that is also modeling.  GMPL doesn't have it.
>>
>> So often, I use GMPL for an initial model - it is a wonderful language, and I find it faster to code than alternatives.  But then when I 'get it right' I have to re-code it in PYOMO or PULP or write directly to an 'lp' file within a Python or C# or other language script.
>>
>> Having the ability to run, adjust variables, add/take away constraints, re-run would be extremely useful, and make GMPL more of a one-stop modeling language.
>>
>> -----Original Message-----
>> From: Help-glpk
>> <[email protected]> On Behalf Of
>> Andrew Makhorin
>> Sent: Sunday, August 23, 2020 2:56 PM
>> To: Domingo Alvarez Duarte <[email protected]>; [email protected]
>> Subject: Re: Adding if/then/else statement to GMPL
>>
>> On Sun, 2020-08-23 at 15:36 +0200, Domingo Alvarez Duarte wrote:
>>> Hello !
>>>
>>> Also I've added the break/continue statements here
>>> https://github.com/mingodad/GLPK/commit/9d70a37b16bd377722eeb3880fcf8
>>> 6
>>> bb3b812118
>>>
>>>
>>> Again any comment/suggestion is welcome !
>>>
>>> Cheers !
>>>
>>>
>>>
>> Please note that GNU MathProg is a *modeling* language; it is not a general-purpose programming language. If you need to produce a non-trivial solution report (since all such-like statements are allowed only on the post-solving stage), it would be more practical to write the solution to a temporary file and then process it with a separate program.
>>
>>
>>
>>
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