Re: [boost] Additions to boost::random

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-01-30 09:35:28

I think Jens is even busier than I am right now, and has gone mostly
incommunicado for a while ;-). If you don't hear from him right away, I
would forge ahead with your idea. It sounds superb to me, FWIW.

-Dave

----- Original Message -----
From: "Matthias Troyer" <troyer_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Wednesday, January 30, 2002 9:27 AM
Subject: [boost] Additions to boost::random

> Dear Jens, dear Booster
>
> We now daily use the boost::random library in our production codes, and
> have collected our experiences with it. As I have heard that the library
> has been proposed as a possible addition to the C++ standard, I wish to
> bring up our experiences, and propose a minor change that would greatly
> help generic programming with boost::random.
>
> The problem we face at the moment is that the arguments to the seed(...)
> function and to the non-default constructor are dependent on the
> generator.
> This makes it impossible to just change generators, without changing
> the code, when the code needs to seed a generator, which happens
> in many applications, e.g. when a new generator needs to be
> spawned dynamically in an application.
>
> One solution would be to always require a seed(uint32_t ). However the
> problem there is that for generators like the LCG many integers are bad
> seed values, and the good/bad values differ from generator to generator.
> Also, a lagged Fibonacci generator, or a Mersenne Twister (MT) needs a
> long
> seed block instead of a single integer.
>
> There are however solutions to this problem, as implemented e.g. in the
> SPRNG library (http://sprng.cs.fsu.edu/). These solutions take a
> "sequence number", a nonnegative integer, and convert it into a good
> seed for lagged Fibonacci generator. Similar algorithms can be
> implemented
> for the MT, or also for LCGs. This makes it possible to write more
> generic
> codes.
>
> Since I do not want to change the semantics of seed(uint32_t) where
> it is avaiable, I propose to add the following members to the generators:
>
>
>    sequence(uint32_t n) ; // seeds the generator with the n-th good seed
>    static const uint32_t max_sequence; // n can take all values
> 0..max_sequence
>                                        // whereever possible this should
> be the
>                                        // largest possible integer
>
> Alternatively we could replace uint32_t by an integral sequence_type,
> to make it more flexible.
>
> Also, these member should be propagated through the adaptors, so that
> they
> can also be seeded in this way.
>
> If this proposal meets with approval, we will start implementing it and
> can
> then present it to Boost for further discussions.
>
> Best regards,
>
> Matthias
>
>
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