Re: [boost] [odeint] Iterator semantics

Subject: Re: [boost] [odeint] Iterator semantics
From: Sergey Mitsyn (svm_at_[hidden])
Date: 2012-07-31 05:47:55

On 29.07.2012 6:31, Dave Abrahams wrote:
>
> on Thu Jul 12 2012, Karsten Ahnert <karsten.ahnert-AT-ambrosys.de> wrote:
>
>> On 07/12/2012 09:52 AM, Mario Mulansky wrote:
>>> On Wed, 2012-07-11 at 23:50 -0700, Jeffrey Lee Hellrung, Jr. wrote:
>>>
>>> I agree that it1 != it2 should be implemented in the sense of
>>> t1+-dt/2 != t2+-dt/2
>>
>> So you are checking for overlap. This looks good and I think it should work.
>
> If I'm understanding correctly what you're saying, making two iterators
> equal if their underlying time ranges overlap would be "evil."  Your
> equality operator would not be transitive, and thus not an equivalence
> relation, and therefore you would not have implemented a conforming
> iterator, and you'd have no right to expect an algorithm that works on
> iterators to work on yours.

IMHO the values of the iterator's underlying time variable would belong 
to "almost" discrete {t0 + n*dt +/- epsilon}, n from Z, where epsilon 
comes from floating point errors and is small. Thus, the distance 
between neighboring values should be no less than (dt-2*epsilon).

I would say a test 'distance(t1,t2) < dt/2' would be transitive if 
epsilon is less than dt/4

That's of course true while t0 and dt is the same for all iterators 
passed to an algorithm.

>
> But maybe in my fast skimming I've failed to grasp what's going on.
>

-- 
------------
Sergey Mitsyn.