Re: Copy construction of TR1 random number engines
On 8 Apr., 20:48, "Chaille" <nah...@karlfeldt.com> wrote:
When I tried out the TR1 random number facility, I stumbled across
something strange. Trying to create two low-correlation sequences gives
different results depending on how I do it! It seems that the cause for
the
problem is that the copy constructors for the random number engines do
actually not create copies holding the identical state, but initializes
the
"copies" with the same initial seed.
[...]
::std::generate_n(::std::back_insert_iterator<Seq>(seq1), 1000, eng);
::std::generate_n(::std::back_insert_iterator<Seq>(seq2), 1000, eng);
// This assert fires
assert(!equal(seq1.begin(), seq1.end(), seq2.begin()));
----8<----
generate_n takes a copy of the engine 'eng' and doesn't modify it. So,
the 2nd copy for the 2nd generate_n will have exactly the same state
as the first copy.
Cheers!
SG
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