Changes between Initial Version and Version 1 of Ticket #10950
 Timestamp:
 03/16/11 18:08:08 (9 years ago)
Legend:
 Unmodified
 Added
 Removed
 Modified

Ticket #10950

Property
Summary
changed from
The Hash function for matrices has many collisions with permutation matrices:
toThe Hash function for matrices suffers from many collisions with permutation matrices

Property
Summary
changed from

Ticket #10950 – Description
initial v1 1 The current hash function for generic dense matrices suffers from hard 2 collisions with permutation matrices. For example: all permutation 3 matrices of size 4 have hash 0! 1 The current hash function for generic dense matrices suffers from hard collisions with permutation matrices. For example: all permutation matrices of size 4 have hash 0! 4 2 5 3 {{{ … … 31 29 32 30 I stumbled on this when profiling some code using Weyl groups that 33 heavily used caching (the hash of a weyl group element is the hash of 34 the underlying matrix). I gained a speed factor of 10x by just 35 tweaking the hash of matrices as in the attached patch. Now, I have no 36 idea if in general that would be a good hash for matrices, so please 37 some expert write an appropriate patch. 31 heavily used caching (the hash of a weyl group element is the hash of the underlying matrix). I gained a speed factor of 10x by just tweaking the hash of matrices as in the attached patch. Now, I have no idea if in general that would be a good hash for matrices, so please some expert write an appropriate patch. 38 32 39 33 Cheers,