Re: [Bug-glpk] Missing documentation {1..100:Uniform01()<.1}

[Heinrich Schuchardt]

On 05.08.2015 07:36, Andrew Makhorin wrote:
> On Tue, 2015-08-04 at 23:34 +0200, Heinrich Schuchardt wrote:
>> Hello Andrew,
>>
>> the following syntax is useful to produce a random set.
>>
>> set J := {1..100:Uniform01()<.1};
>> display J;
>> end;
>>
>> Unfortunately gmpl.pdf does not describe when random number are
>> evaluated in indexing expression.
> 
> Clause 3.1.5 "Function references", p. 14, explains how pseudo-random
> generator functions are evaluated.

"Note that each pseudo-random generator function has a latent argument
(i.e. some internal state), which is changed whenever the function has
been applied. Thus, if the function is applied repeatedly even to
identical arguments, due to the side effect different resultant values
are always produced."

The sentence describes that if Uniform01 is "applied" 100 times it may
yield 100 different results.

The sentence does not describe how often Uniform01 is "applied" in
{1..100:Uniform01()<.1}. It could be once or 100 times.

Best regards

Heinrich

> 
>>
>> Please, add a sentence like
>> "If the predicate of the indexing expression depends on a random
>> function, it will be evaluated for every index combination individually."
>>
>> Best regards
>>
>> Heinrich Schuchardt
>>
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> 
> 
>