[Octave-bug-tracker] [bug #50426] perms() sort order different than Matlab

[Nicholas Jankowski]

Follow-up Comment #23, bug #50426 (project octave):

still recompiling to test, but looking through the BISTs for the new perms,
some don't seem to be matching the compatible ordering.

lexicographical ordering basically results in the sorted number increasing at
each step. so the reverse of that has the lowest number at the bottom, highest
at the top.

e.g., 


>> perms([1 2])
ans =

     2     1
     1     2

>> perms([1 2 3])
ans =

     3     2     1
     3     1     2
     2     3     1
     2     1     3
     1     3     2
     1     2     3


the new behavior means that pattern should be matched based on input order,
not input values. e.g.:

%!assert (perms ([pi, e]), [pi, e; e, pi])

should be changed to:

%!assert (perms ([pi, e]), [e, pi; pi, e])

similarly, the point of the reopened report is that 

perms(1:5) and perms ([2 5 4 1 3]) shouldn't give the same result, so %!assert
(perms (1:5), perms ([2 5 4 1 3]'))

should no longer pass. what they should produce:


>> a = perms(1:5);
>> a(end-10:end,:)

ans =

     1     3     5     2     4
     1     3     4     5     2
     1     3     4     2     5
     1     3     2     5     4
     1     3     2     4     5
     1     2     5     4     3
     1     2     5     3     4
     1     2     4     5     3
     1     2     4     3     5
     1     2     3     5     4
     1     2     3     4     5

>> a = perms([2 5 4 1 3]);
>> a(end-10:end,:)

ans =

     2     4     3     5     1
     2     4     1     3     5
     2     4     1     5     3
     2     4     5     3     1
     2     4     5     1     3
     2     5     3     1     4
     2     5     3     4     1
     2     5     1     3     4
     2     5     1     4     3
     2     5     4     3     1
     2     5     4     1     3




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