Re: Multi problems in GMPL
Dear Domingo, I share the opinion that GMPL should remain a domain-specific language, and the additions that are being proposed would fit better in a general-purpose language. This was the intention of the package python-glpk (discontinued after some internal changes in glpk), which has been captured and extended in AMPL's Python interface, AMPLPY: https://amplpy.readthedocs.io/en/latest/ Some examples there are similar to what you propose. Cheers, Joao Pedro
Re: Adding if/then/else statement to GMPL
Hello Andrew !
After replying to your last email I came with this possible solution to
allow multiple solve statements in GMPL:
https://github.com/mingodad/GLPK/commit/b80bcd86f1a78eba753e919a56fb9b976934b237
Cheers !
On 27/8/20 11:44, Domingo Alvarez Duarte wrote:
Hello Andrew !
Thanks for reply !
You are right in respect to the original implementation, one possible
way to have multiple solve statements working is to pause the
execution return a code that would tell the caller to generate the
problem, solve it, postsolve and then continue the execution from that
point (glpsol is somehow already doing it but is not looping back to
see if there is more solve statements to execute).
Anyone can contribute to make this work !
Pseudo code:
=
/* generate the model */
while ((ret = glp_mpl_generate(csa->tran, csa->out_dpy)) ==
GMPL_SOLVE)
{
if (glp_mpl_generate(csa->tran, csa->out_dpy)) goto err2;
/* build the problem instance from the model */
glp_mpl_build_prob(csa->tran, csa->prob);
...
glp_simplex(csa->prob, &csa->smcp);
...
glp_intopt(csa->prob, &csa->iocp);
...
ret = glp_mpl_postsolve(csa->tran, csa->prob, GLP_SOL);
//resume the execution
}
=
Cheers !
On 27/8/20 11:25, Andrew Makhorin wrote:
On Thu, 2020-08-27 at 11:01 +0200, Domingo Alvarez Duarte wrote:
Hello !
I just finished adding the parsing code to parse this dummy model:
https://github.com/mingodad/GLPK/blob/local-set-param/examples/cut2.mo
d
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] = 0.17
price[45] = 0.416667
price[50] = 0.5
price[55] = 0.5
price[75] = 0.83
Model has been successfully generated
>Exit code: 0
=
Cheer !
repeat {
solve Cutting_Opt;
let {i in WIDTHS} price[i] := Fill[i].dual;
display price;
solve Pattern_Gen;
if Reduced_Cost < -0.1 then {
let nPAT := nPAT + 1;
let {i in WIDTHS} nbr[i,nPAT] := Use[i];
display Use;
}
else break;
}
I don't think that the solve statement is executed more than once.
Internally the solve statement is not a real statement (like display),
i.e. it doesn't "call" a solver; it is just a marker that separates the
main part and the post-solving part of the model.
Re: Adding if/then/else statement to GMPL
Hello Andrew !
Thanks for reply !
You are right in respect to the original implementation, one possible
way to have multiple solve statements working is to pause the execution
return a code that would tell the caller to generate the problem, solve
it, postsolve and then continue the execution from that point (glpsol is
somehow already doing it but is not looping back to see if there is more
solve statements to execute).
Anyone can contribute to make this work !
Pseudo code:
=
/* generate the model */
while ((ret = glp_mpl_generate(csa->tran, csa->out_dpy)) ==
GMPL_SOLVE)
{
if (glp_mpl_generate(csa->tran, csa->out_dpy)) goto err2;
/* build the problem instance from the model */
glp_mpl_build_prob(csa->tran, csa->prob);
...
glp_simplex(csa->prob, &csa->smcp);
...
glp_intopt(csa->prob, &csa->iocp);
...
ret = glp_mpl_postsolve(csa->tran, csa->prob, GLP_SOL);
//resume the execution
}
=
Cheers !
On 27/8/20 11:25, Andrew Makhorin wrote:
On Thu, 2020-08-27 at 11:01 +0200, Domingo Alvarez Duarte wrote:
Hello !
I just finished adding the parsing code to parse this dummy model:
https://github.com/mingodad/GLPK/blob/local-set-param/examples/cut2.mo
d
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] = 0.17
price[45] = 0.416667
price[50] = 0.5
price[55] = 0.5
price[75] = 0.83
Model has been successfully generated
>Exit code: 0
=
Cheer !
repeat {
solve Cutting_Opt;
let {i in WIDTHS} price[i] := Fill[i].dual;
display price;
solve Pattern_Gen;
if Reduced_Cost < -0.1 then {
let nPAT := nPAT + 1;
let {i in WIDTHS} nbr[i,nPAT] := Use[i];
display Use;
}
else break;
}
I don't think that the solve statement is executed more than once.
Internally the solve statement is not a real statement (like display),
i.e. it doesn't "call" a solver; it is just a marker that separates the
main part and the post-solving part of the model.
Re: Adding if/then/else statement to GMPL
On Thu, 2020-08-27 at 11:01 +0200, Domingo Alvarez Duarte wrote:
> Hello !
>
> I just finished adding the parsing code to parse this dummy model:
>
> https://github.com/mingodad/GLPK/blob/local-set-param/examples/cut2.mo
> d
>
> 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] = 0.17
> price[45] = 0.416667
> price[50] = 0.5
> price[55] = 0.5
> price[75] = 0.83
> Model has been successfully generated
> >Exit code: 0
>
> =
>
> Cheer !
>
>
> repeat {
> solve Cutting_Opt;
> let {i in WIDTHS} price[i] := Fill[i].dual;
> display price;
>
> solve Pattern_Gen;
> if Reduced_Cost < -0.1 then {
> let nPAT := nPAT + 1;
> let {i in WIDTHS} nbr[i,nPAT] := Use[i];
> display Use;
> }
> else break;
> }
I don't think that the solve statement is executed more than once.
Internally the solve statement is not a real statement (like display),
i.e. it doesn't "call" a solver; it is just a marker that separates the
main part and the post-solving part of the model.
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] = 0.17 price[45] = 0.416667 price[50] = 0.5 price[55] = 0.5 price[75] = 0.83 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 Sent: Monday, August 24, 2020 10:34 AM To: Meketon, Marc ; Andrew Makhorin ; help-glpk@gnu.org 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 On Behalf Of Andrew Makhorin Sent: Sunday, August 23, 2020 2:56 PM To: Domingo Alvarez Duarte ; help-glpk@gnu.org 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. This e-mail and any attachments may be confidential or legally privileged. If you received this message in error or are not the intended recipient, you should destroy the e-mail message and any attachments or copies, and you are prohibited from retaining, distributing, disclosing or using any information contained herein. Please inform us of the erroneous delivery by return e-mail. Thank you for your cooperation. This e-mail and any attachments may be confidential or legally privileged. If you received this message in error or are not the intended recipient, you should destroy the e-mail message and any attachments or copies, and you are prohibited from retaining, distributing, disclosing or using any information contained herein. Please inform us of the erroneous delivery by return e-mail. Thank you for your cooperation.
