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From Gilles <gil...@harfang.homelinux.org>
Subject Re: [math] random boolean arrays
Date Sat, 11 Jul 2015 22:38:03 GMT
On Sat, 11 Jul 2015 15:12:29 -0700, Phil Steitz wrote:
> On 7/11/15 3:06 PM, Gilles wrote:
>> On Sat, 11 Jul 2015 12:08:16 -0700, Phil Steitz wrote:
>>> The code implemented in MATH-1242 to improve performance of KS
>>> monteCarloP in-lines efficient generation of random boolean arrays.
>>>   Unfortunately, I think the implementation is not quite random 
>>> (see
>>> comments on the ticket).  To verify it, we need to be able to test
>>> the random boolean array generation directly.  To do that, we have
>>> to either expose the method (at least as protected) in the KS class
>>> or add it somewhere else.  I propose the latter but am not sure
>>> where to put it.  For speed, we need to avoid array copies, so the
>>> API will have to be something like randomize(boolean[], nTrue).
>>
>> Are you sure that copying is an issue for speed?
>> I mean, the randomization will anyways copy new values into the
>> array...
>
> The algorithm is used in a tight loop that would be slowed down
> considerably by allocating and copying arrays to / from the stack.

Numbers?
IIRC, someone said: "First make it correct, then make it faster (if
necessary)". [I.e. the computation may always be inlined later.]

[And I don't get the "copying to / from the stack"...]

Gilles

>>> It
>>> could go in the swelling MathArrays class, or RandomDataGenerator.
>>> The latter probably makes more sense, but the API does not fit too
>>> well.  Any ideas?
>>
>> Isn't there some relationship with
>>   https://issues.apache.org/jira/browse/MATH-1158
>> ?
>
> No.
>
> Phil
>>
>>
>> Gilles


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