[Octave-bug-tracker] [bug #43041] isprime(5i) returns true

[Rik]

Follow-up Comment #4, bug #43041 (project octave):

Is it correct to return 


isprime (abs (x))


when x is real and less than 0?  Every web source defines a real-valued prime
on the positive integer range [1, Inf].  As an example,
http://mathworld.wolfram.com/PrimeNumber.html.

It seems to be more appropriate to issue an error in this case.  Or, if the
calculation should proceed then to issue NaN since it is not definitionally a
prime number, even if it meets the test for being a prime.

In this case, -5, looks like a duck, quacks like a duck, but is excluded by
definition from actually being a duck.




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