Re: [boost] Problem with boost::random seed

Subject: Re: [boost] Problem with boost::random seed
From: Anton Skvorts (anton.skvorts_at_[hidden])
Date: 2011-01-25 20:28:25

Many thanks for your advice. Now it works fine!

2011/1/25 Steven Watanabe <watanabesj_at_[hidden]>

> AMDG
>
>
> On 1/24/2011 11:29 AM, Anton Skvorts wrote:
>
>> Testing boost::random with the following code
>>
>> boost::mt19937 gener(1);
>> boost::normal_distribution<>  normal(0,1);
>> boost::variate_generator<boost::mt19937&,boost::normal_distribution<>  >
>> rng(gener, normal);
>> cout<<  rng()<<  endl;
>> cout<<  rng()<<  endl;
>> cout<<  rng()<<  endl;
>> gener.seed(2);
>> cout<<  rng()<<  endl;
>> cout<<  rng()<<  endl;
>> cout<<  rng()<<  endl;
>>
>> I'm getting unexpected values after gener.seed(2)
>>     -2.971829031 1.706951063 -0.430498971
>>
>>     -2.282022417  x
>>  -0.5887503675
>>  0.2504171986
>>
>> The value -2.282022417 is the forth number in the sequence originated by
>> gener(1) and not the first number in the sequence originated by
>> gener.seed(2)
>> as one would expect (this number is  actually -0.5887503675). If I reseed
>> next with gener.seed(3)it works fine, but if after that I reseed again
>> with
>> gener.seed(1) I'll get the same problem, and so on and off...
>>
>> How can I reseed the random number generator to overcome this problem?
>>
>>
> This is because normal_distribution uses Box-Muller,
> which generates pairs of normal variates.  You need
> to call rng.distribution().reset() to clear the cached
> result.
>
> In Christ,
> Steven Watanabe
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