Dear all,
I am running Sage Version 4.8 with combinat compiled 3 days ago.
I was trying to compute the class of extended B-matices for the principal
coefficients cluster algebra of type $E_8$ and I got the following error.
sage: S=ClusterSeed(['E',8])
sage: T=S.principal_extension()
sage: T.b_matrix_class()
---------------------------------------------------------------------------
IndexError Traceback (most recent call
last)
/home/plutone/staff/stella/sage-4.8/<ipython console> in <module>()
/home/plutone/staff/stella/sage-4.8/local/lib/python2.6/site-packages/sage/combinat/cluster_algebra_quiver/cluster_seed.pyc
in b_matrix_class(self, depth, up_to_equivalence)
1474 assert self.is_mutation_finite(), 'The B-matrix
class can - for infinite mutation types - only be computed up to a given depth'
1475
-> 1476 return [ M for M in self.b_matrix_class_iter(
depth=depth, up_to_equivalence=up_to_equivalence ) ]
1477
1478 def variable_class_iter(self, depth=infinity,
ignore_bipartite_belt=False):
/home/plutone/staff/stella/sage-4.8/local/lib/python2.6/site-packages/sage/combinat/cluster_algebra_quiver/cluster_seed.pyc
in b_matrix_class_iter(self, depth, up_to_equivalence)
1450 """
1451 Q = self.quiver()
-> 1452 for M in Q.mutation_class_iter( depth=depth,
up_to_equivalence=up_to_equivalence, data_type='matrix' ):
1453 yield M
1454
/home/plutone/staff/stella/sage-4.8/local/lib/python2.6/site-packages/sage/combinat/cluster_algebra_quiver/quiver.pyc
in mutation_class_iter(self, depth, show_depth, return_paths, data_type,
up_to_equivalence, sink_source)
917 dg = DiGraph( self._digraph )
918 MC_iter = _mutation_class_iter( dg, self._n, self._m,
depth=depth, return_dig6=return_dig6, show_depth=show_depth,
up_to_equivalence=up_to_equivalence, sink_source=sink_source )
--> 919 for data in MC_iter:
920 if data_type == "quiver":
921 Q = Quiver( data[0] )
/home/plutone/staff/stella/sage-4.8/local/lib/python2.6/site-packages/sage/combinat/cluster_algebra_quiver/mutation_class.pyc
in _mutation_class_iter(dg, n, m, depth, return_dig6, show_depth,
up_to_equivalence, sink_source)
167 nr_mutations = 1
168 if up_to_equivalence:
--> 169 iso, orbits = _dg_canonical_form( dg, n, m )
170 iso_inv = dict( (iso[a],a) for a in iso )
171
/home/plutone/staff/stella/sage-4.8/local/lib/python2.6/site-packages/sage/combinat/cluster_algebra_quiver/mutation_class.pyc
in _dg_canonical_form(dg, n, m)
143 if v >= n:
144 del iso[v]
--> 145 v1,v2,label1 = [ edge for edge in
dg._backend.iterator_in_edges([v],True) ][0]
146 w1,w2,label2 = [ edge for edge in
dg._backend.iterator_out_edges([v],True) ][0]
147 dg._backend.del_edge(v1,v2,label1,True)
IndexError: list index out of range
The same error reproduces in may other cases of principal extensions. Is
there some issue with dg._backend.iterator_in_edges for rectangular matrices?
Adding the flag up_to_equivalence=False to b_matrix_class I get the expected
answer (I assume this flag prevent _dg_canonical_form from running) but my
hardware is too small to handle the case $E_8$ without the reduction up to
equivalece.
Is there any workaround for this problem?
Thanks
S.
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