[Octave-bug-tracker] [bug #60928] Performance of sort unexpectedly slow for DIM=2

[Rik]

Update of bug #60928 (project octave):

                  Status:                    None => Confirmed              
                 Summary: Performance of sort, not sure if this is expected
behavior? => Performance of sort unexpectedly slow for DIM=2

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Follow-up Comment #1:

Confirmed.  This is really odd behavior that seems to be limited to sorting
along the second dimension.  I modified your test code to look at sorting
along each dimension.


data = rand (5,3,5e4);
tic; s2 = sort (data, 1); bm_sort = toc
#tic; s2 = sort (data, 2); bm_sort = toc
#tic; s2 = sort (data, 3); bm_sort = toc
perm = [1 2 3];
#perm = [2 1 3];
#perm = [3 2 1];
tic; s1 = ipermute (sort (permute (data, perm), 1), perm); bm_perm = toc
if (! isequal (s1, s2))
  disp ("s1 != s2");
endif


Timings for sorting along dimension 1 are already strange.


bm_sort = 0.016349
bm_perm = 0.011381


In this case, the benchmark for the permute strategy has a call to permute(),
the exact same call to sort(), and a call to ipermute().  How can that take
less time then the single call to sort?

Timing for dimension 2 are the real issue.


bm_sort = 3.8263
bm_perm = 0.016575


The call to sort() is 231X slower than using the permute strategy.

Finally, sorting on dimension 3 seems about the same.


bm_sort = 0.085065
bm_perm = 0.072229




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