[Octave-bug-tracker] [bug #54619] randi() is biased

[anonymous]

Follow-up Comment #4, bug #54619 (project octave):

There is a correct way to generate random integers in a given range, and there
are incorrect ways. The method that I linked is the correct way. Other ways
are incorrect. The bias might be small, but it's there.

GNU's C++ Standard Library does it right also:


const __uctype __uerange = __urange + 1; // __urange can be zero
const __uctype __scaling = __urngrange / __uerange;
const __uctype __past = __uerange * __scaling;
do
   __ret = __uctype(__urng()) - __urngmin;
while (__ret >= __past);
__ret /= __scaling;


No serious scientific software would use the method used by Octave. This is
why I'm reporting it as a bug. Take it or leave it.

Note that random floating-point numbers are totally different from random
integers, and should not be used as a comparison. And they should not be used
as a basis either.

This "large project" is just throwing away randmtzig.cc and replacing that
with stuff from the Standard Library
<https://en.cppreference.com/w/cpp/header/random>. Random number generation is
complicated enough that one should not attempt to reinvent the wheel.


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