forum.polymake.org

Posted: **12 Mar 2024, 16:05**

Hi,
when I print facets of a polytope, according to documentation I should get a matrix of numbers, each rows represents one inequality with the numbers being the coeficients in the respective inequality. However, I get this:

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> $c = cube(3,0);
> print $c->FACETS;
(4) (1 1)
1 -1 0 0
(4) (2 1)
1 0 -1 0
(4) (3 1)
1 0 0 -1

How should I interpret this output and why does it look like this? Is it possible to force the output to adhere to the format from the docs?

For the context, I need to use polymake to convert polytopes from V-repre to H-repre, where the H-repre will need to be saved as CPLEX .lp format and lrs/cdd .ine format (but I can convert to these manually if I have the matrix representation).

Posted: **12 Mar 2024, 16:16**

The (dim) (key value) ... style is for sparse vectors / matrices where the first entry is the length and each following pair is index and value. You can force the default output with dense:

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polytope > print dense($c->FACETS);
0 1 0 0
1 -1 0 0
0 0 1 0
1 0 -1 0
0 0 0 1
1 0 0 -1

Regarding .lp output you can also have a look at poly2lp: https://polymake.org/doku.php/documenta ... pe#poly2lp

Best
Benjamin

Posted: **12 Mar 2024, 17:31**

Thank you!

I tried both poly2lp and and poly2porta (since I kinda work with it too) and they didn't work.
Running

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poly2lp($c)

gave me

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polymake: WARNING: available properties insufficient to compute 'LP'

while poly2porta gives

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polymake: ERROR: Undefined subroutine &Polymake::User::poly2porta called

Posted: **12 Mar 2024, 18:15**

poly2lp requires an LP for the objective function, either as a subobject or as a second argument, e.g.:

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polytope > $c = cube(3);

polytope > $lp = $c->LP(LINEAR_OBJECTIVE=>[0,1,1,1]);

polytope > poly2lp($c, $lp);
MINIMIZE
  obj: +1 x1 +1 x2 +1 x3
Subject To
  ie0: +1 x1 >= -1
  ie1: -1 x1 >= -1
  ie2: +1 x2 >= -1
  ie3: -1 x2 >= -1
  ie4: +1 x3 >= -1
  ie5: -1 x3 >= -1
BOUNDS
  x1 free
  x2 free
  x3 free
END

For poly2porta you need to make sure the porta.rules are active:

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polytope > reconfigure "porta.rules";
Could not find the program `xporta' anywhere along your PATH.
Please enter the full path or an empty string to abort.
[program path] > xporta

polytope > poly2porta($c,"portafile");

polytope > exit;
$ cat portafile 
DIM=3
CONV_SECTION
-1 -1 -1
1 -1 -1
-1 1 -1
1 1 -1
-1 -1 1
1 -1 1
-1 1 1
1 1 1
END

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Output format of FACETS

Output format of FACETS

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Re: Output format of FACETS