[Octave-bug-tracker] [bug #61199] Allow 'char' input sets to nchoosek for Matlab compatibility

[Rik]

Follow-up Comment #24, bug #61199 (project octave):

@Anonymous: Matlab gives no warnings for nchoosek (54,27) and nchoosek
(56,28).  The results are the same for Matlab and for unpatched Octave, so it
is not clear that the improved code with gcd() is necessary for these cases.

In Matlab, nchoosek (58,29) does produce a warning.  Specifically, "Warning:
Result may not be exact.  Coefficient is greater than 9.007199e15 and is only
accurate to 15 digits.

The result is the same in either Matlab or Octave


format long
z = nchoosek (58,29)
z = 3.006726649954106e+16
+verbatim-

With the patched code that uses gcd() the answer differs by 2 in the last
position


z = 3.006726649954104e+16


There are some differences.  For Matlab and Octave unpatched code,


nchoosek (56,26)
ans = 6.646448384109071e+15


BUT, for patched code


nchoosek (56,26)
ans = 6646448384109072


There is a difference of 1 in the final position.  This is correct as the
answer should be even.  But, is it worth it?  eps (6.646448384109071e+15) is 1
so essentially the current calculation is within the error bar for a numerical
approximation.  I don't have much of an opinion here.

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