internal casting for LatticePolytope does not work in shell?

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tran.mai.ngoc
Posts: 3
Joined: 04 Nov 2017, 16:59

internal casting for LatticePolytope does not work in shell?

Postby tran.mai.ngoc » 04 Nov 2017, 17:04

Hi,
I'm using the online polymake
https://shell.polymake.org/

I have a lattice polytope, and I need to check if it is smooth.
The polytope is:
$C3 = new Polytope(POINTS =>[[1,1,0,0,0,0,0,0,0,0], [1,0,0,0,0,1,0,0,0,0],
[1,0,0,0,0,0,0,0,0,1],
[1,1,1,0,1,1,0,0,0,0],
[1,1,0,1,0,0,0,1,0,1],
[1,0,0,0,0,1,1,0,1,1],
[1,1,1,1,1,1,1,1,1,1],[1,0,0,0,0,0,0,0,0,0]]);

$C3->LATTICE
returns 1, but I cannot get it casted to to Polytope<LatticePolytope>

(ie: the $C3->REFLEXIVE trick did not work. $C3->SMOOTH just returns nothing).

I've tried the example with the cube:
https://polymake.org/doku.php/tutorial/ ... s_tutorial
ie:

$p = cube(3);
$p->type->full_name;
$p->LATTICE;
$p->REFLEXIVE;
$p->type->full_name;

but in the end the polytope type is still Polytope<Rational>
however, the command
print $p->SMOOTH;
still works, so that is quite mysterious.

Could you please let me know how I can explicitly cast a polytope as a LatticePolytope?
(And shouldn't the casting be done after one runs $C3->LATTICE?)

User avatar
joswig
Main Author
Posts: 215
Joined: 24 Dec 2010, 11:10

Re: internal casting for LatticePolytope does not work in shell?

Postby joswig » 08 Nov 2017, 11:36

Your polytope is low-dimensional. Therefore, it is not reflexive by definition (at least in the sense of polymake).

Code: Select all

polytope > print $C3->DIM; 6 polytope > print $C3->AMBIENT_DIM; 9 polytope > print $C3->REFLEXIVE;
I agree that no output is not very encouraging. But it actually works alright:

Code: Select all

polytope > if (!$C3->REFLEXIVE) { print "not reflexive" } not reflexive
We should consistently change the output to 0 to indicate false.

Sorry for the inconvenience.

User avatar
joswig
Main Author
Posts: 215
Joined: 24 Dec 2010, 11:10

Re: internal casting for LatticePolytope does not work in shell?

Postby joswig » 08 Nov 2017, 11:48

To actually answer your question: that type LatticePolytope is a relic from ancient polymake times. It is not needed any more, but it still somehow exists in some dark corners for backward compatibility. You just need the Polytope<Rational> type, and if LATTICE gives true, then it is a lattice polytope.

If you do not want to have that checked by polymake, it is legal to specify this on input:

Code: Select all

polytope > $square = new Polytope(POINTS=>[[1,0,0],[1,1,0],[1,0,1],[1,1,1]], LATTICE=>1);
But in this case you are responsible for the correctness. That is to say, polymake does not complain about the following:

Code: Select all

polytope > $badquadrangle = new Polytope(POINTS=>[[1,0,0],[1,1,0],[1,0,1],[1,4/3,6/7]], LATTICE=>1);
So it may give you inconsistent output later. This behavior is not by accident but rather by design.


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