[Octave-bug-tracker] [bug #53434] isprime.m:missing error, warning for negative numbers

[Michael Leitner]

Follow-up Comment #5, bug #53434 (project octave):

To answer your previous question, because (-2+1i)*(-1-2i)=(4+3i), while for
8+3i no such factorization can be found, because if there were two Gaussian
integers that have the product 8+3i, their absolute values would need to have
the product sqrt(73). However, 73 is a prime number, and as the absolute value
of any Gaussian integer is the square root of an integer, one of these factors
would need to have an absolute value of 1. Thus 8+3i is prime. Or you just
believe the 19-th century number theoreticians.

To answer why it is not following Matlab: browse the source code to look when
this has been introduced. I just did this exercise for you, giving the result
that you should check the discussion at bug #43041. If this is dear to your
heart, you can try to see whether the consensus has changed in the meantime.

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