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Subject: Re: [Boost-users] [Random] normal distribution different behaviour 1.55 vs 1.57
From: Thomas M (firespot71_at_[hidden])
Date: 2014-12-21 16:23:45

On 19/12/2014 12:56, Neal Becker wrote:
> oswin krause wrote:
>> On 19.12.2014 00:00, Semen Trygubenko / Семен Тригубенко wrote:
>>> On the positive side, our tests are now much more robust to that sort
>>> of changes. :)
>> We had the same issue a few years ago when changing to boost::random -
>> almost every test broke. It turned out that testing for specific values
>> or only a small number of samples (the only tests which are affected by
>> this kind of change) can mask a lot of bugs - even though some values
>> seem to be correct, confidence intervals or measured variances can still
>> be off. So for us a more robust test also meant a better test that
>> discovered bugs.
>> But yeah: such a change should be part of the change-log.
>> _______________________________________________
> Not sufficient! Any such change should be discussed with the boost user
> community first. Boost should have a policy that any breaking changes are
> discussed on boost-dev.

I second that, first the proposal should be discussed, and if
implemented become very loudly announced in the change-logs.

For what it's worth I believe it should have even been possible to
add/offer different variates generation algorithms (for any
distribution) without breaking current behaviour: an extra template
argument (to the distribution itself), with the current algorithm as
default type, and here we'd have (almost) the best of both worlds. Again
a discussion with the community beforehand would be useful.

As to making tests simply robust: out of the box I can come up (from own
work, real-world) with cases when this is not possible, e.g. when
obtaining a non-small sample takes a looong time (> weeks; sorry not
waiting that long to test boost), or when there's no way around truly
comparing values for [floating-point near-] equality.


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