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Posted: **28 Apr 2017, 11:52**

I have a small problem with face lattices of polytopes. The following code from the tutorial (https://polymake.org/doku.php/tutorial/ ... e_tutorial) does not work anymore:

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$p = n_gon(5);
$HD = $p->HASSE_DIAGRAM;
for (my $k=$HD->DIMS->[1]; $k<$HD->DIMS->[2]; ++$k) { print $HD->FACES->[$k] }

Here is the error that I get from both my local polymake and the web interface:

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polytope > $p = n_gon(5);
polytope > $HD = $p->HASSE_DIAGRAM;
polymake: used package ppl
  The Parma Polyhedra Library (PPL): A C++ library for convex polyhedra
  and other numerical abstractions.
  http://www.cs.unipr.it/ppl/
polytope > for (my $k=$HD->DIMS->[1]; $k<$HD->DIMS->[2]; ++$k) { print $HD->FACES->[$k] }
polymake:  WARNING: available properties insufficient to compute 'DIMS'
polymake:  ERROR: Can't use an undefined value as an ARRAY reference at input line 1.

The face lattice is incredibly useful for computing resolution of certain classes of hypersurface singularities.

Posted: **28 Apr 2017, 15:10**

Thanks for pointing this out. The tutorial will be corrected.

The property DIMS was sacrificed in the last refactoring. This is now replaced by a more fancy mechanism. E.g., you can do

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print $HD->INVERSE_RANK_MAP->nodes_of_rank(2);

to obtain the indices of the faces of rank 2 (i.e., the edges). The resulting numbers can be applied as indices, i.e., to the DECORATION property.

Posted: **28 Apr 2017, 15:21**

The tutorial is now updated.

There is also a shortcut to get the nodes of a given dimension (in contrast to the rank):

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print $p->HASSE_DIAGRAM->nodes_of_dim(1);

Or printing the faces (and this should work with both 3.0 and 3.1):

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print map { $p->HASSE_DIAGRAM->FACES->[$_] } @{$p->HASSE_DIAGRAM->nodes_of_dim(1)};

Posted: **28 Apr 2017, 15:22**

Thanks alot, that will make my code even cleaner now. I was wondering how to obtain the decorations...

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Face lattices of polytopes

Face lattices of polytopes

Re: Face lattices of polytopes

Re: Face lattices of polytopes

Re: Face lattices of polytopes