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: sage-combinat
Priority: major Milestone: sage-6.8
Component: combinatorics Keywords: crystals, tensor product
Cc: sage-combinat, 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:

Status badges


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(k-1). 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 tscrim

  • Branch set to public/crystals/fix_tensor_product-18469
  • Commit set to 211f6116ff935d05994f64801950715eea591922
  • Status changed from new to needs_review

New commits:

211f611Fixing _sig for epsilon/phi returning -inf.

comment:2 Changed 7 years ago by git

  • Commit changed from 211f6116ff935d05994f64801950715eea591922 to 9a24ea03c2a5a4268224cc34230681bbb8b92190

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

9a24ea0Fixing _sig for epsilon/phi returning -inf.

comment:3 Changed 7 years ago by bsalisbury1

  • Reviewers set to Ben Salisbury
  • Status changed from needs_review to positive_review

Thanks, Travis.

comment:4 Changed 7 years ago by vbraun

  • Branch changed from public/crystals/fix_tensor_product-18469 to 9a24ea03c2a5a4268224cc34230681bbb8b92190
  • Resolution set to fixed
  • Status changed from positive_review to closed
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