Opened 7 years ago
Closed 7 years ago
#18469 closed defect (fixed)
Tensor product of crystals does not handle inf for epsilon/phi correctly
Reported by:  tscrim  Owned by:  sagecombinat 

Priority:  major  Milestone:  sage6.8 
Component:  combinatorics  Keywords:  crystals, tensor product 
Cc:  sagecombinat, bsalisbury1, aschilling  Merged in:  
Authors:  Travis Scrimshaw  Reviewers:  Ben Salisbury 
Report Upstream:  N/A  Work issues:  
Branch:  9a24ea0 (Commits, GitHub, GitLab)  Commit:  9a24ea03c2a5a4268224cc34230681bbb8b92190 
Dependencies:  Stopgaps: 
Description
This does not work:
sage: E1 = crystals.elementary.B(['A',2], 1) sage: E2 = crystals.elementary.B(['A',2], 2) sage: T = crystals.TensorProduct(E1, E2) sage: x = T(E1.module_generators[0], E2.module_generators[0]); x [0, 0] sage: x.f(1) [1, 0] sage: x.e(1) [1, 0]
The reason is because we try and be clever with how we compute the _sig
and do an epsilon_(k)  phi_i(k1)
. If one of these (in particular, the phi) is inf
, then the computation breaks down. Instead, we have to bite the bullet and do the partial sums of the weight pairings to make sure we cover these cases.
Change History (4)
comment:1 Changed 7 years ago by
 Branch set to public/crystals/fix_tensor_product18469
 Commit set to 211f6116ff935d05994f64801950715eea591922
 Status changed from new to needs_review
comment:2 Changed 7 years ago by
 Commit changed from 211f6116ff935d05994f64801950715eea591922 to 9a24ea03c2a5a4268224cc34230681bbb8b92190
Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:
9a24ea0  Fixing _sig for epsilon/phi returning inf.

comment:3 Changed 7 years ago by
 Reviewers set to Ben Salisbury
 Status changed from needs_review to positive_review
Thanks, Travis.
comment:4 Changed 7 years ago by
 Branch changed from public/crystals/fix_tensor_product18469 to 9a24ea03c2a5a4268224cc34230681bbb8b92190
 Resolution set to fixed
 Status changed from positive_review to closed
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New commits:
Fixing _sig for epsilon/phi returning inf.