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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [math] Monitoring iterative algorithms
Date Tue, 09 Aug 2011 15:46:47 GMT
Le 09/08/2011 09:28, Phil Steitz a écrit :
> On 8/8/11 10:46 PM, Sébastien Brisard wrote:
>> 2011/8/8 Phil Steitz<phil.steitz@gmail.com>:
>>> +1 to the idea of using the Observer pattern; but -0 for
>>> Observable.  I would favor defining Events and Listeners because a)
>>> Observable is concrete, so effectively forces you to create an
>>> Observable delegate
>>>
>> I'm not sure I understand. Components in java.awt also need to
>> implement quite a few methods like addListener, fireEvent, and so on.
>> Maybe we could write a DefaultObservable, which would implement most
>> of the methods required by Observable, and could be inherited by some
>> (probably not all, unfortunately) of the already implemented iterative
>> algorithms ?
>
> I was suggesting that we dispense with having anything inherit from
> Observable and just define events and listeners, similarly to what
> you find in the awt components, but also elsewhere like javax.sql or
> javax.servlet (and I am sure lots of other places too).  Observable
> just gives you hasChanged and a primitive, non-type-safe
> notifyListeners.  To do proper event propagation you need to define
> custom events anyway and register listeners, so unless all you need
> to raise are "some state has changed" events (like what a GUI
> presentation layer needs from the model in MVC), you are better off
> implementing a proper event framework.  This does not have to be
> heavyweight.  Just define
>
> 0) Event class(es) extending j.u.EventObject
> 1) a listener interface extending j.u.EventListener
> 2) implement addXxxListener, removeXxxListener and
> fireInterstingEvent1...n in the class that you want to be observable
> (i.e. source events)
>
> Items 0) and 1) and most of 2) are going to be necessary anyway if
> you want to propagate typesafe events.  All that you really save by
> bringing in Observable is maintenance of the listener collection,
> which is trivial.
>
> <snip/>
>
>> Browsing through the JavaDoc, I realized that o.a.c.m.ode has some
>> event handling facilities. Is the implementer still around?
>
> That would be Luc.

I'm here.
Sorry for the delay, I am on holidays for three weeks and working in my 
house.

When I read the first mail in this thread a few minutes ago, I thought: 
this is close to what we have in ODE. Then I remembered a discussion 
with Dietmar and Nikolaus when we met at an optimization workshop in 
Toulouse: they also raised the need for some monitoring/logging facility 
in optimization algorithms. Gilles also raise this problem in this thread.

So I would now say: we do have both an event framework *and* a step 
handler framework in ODE, but they are both tailored for ODE.
If we can think of a more general framework, I would say this framework 
should be used for all our iterative algorithms and the ODE framework 
should be changed to use it too.

So here are the needs for ODE:
  - callbacks for regular steps when they complete, without
    any feedback with the algorithm. This is now implemented using
    StepHandler and FixedStepHandler and the handlerStep method is void,
    so from the algorithm point of view this monitoring is almost no-op.
  - callbacks for discrete events, which may provide feedback to the
    algorithm. This is now implemented using EventHandler and requires
    a function to define the event (the g function, events occurring at
    sign changes) and a function to be triggered when the events occurs
    (the eventOccurred function, which provides the current state and
    which return value is used by the algorithm to know what to do next,
    i.e. continue/stop/reset state/reset derivatives.

These needs are really, really important and in fact are one of the main
feature in Commons Math ODE (and prior to that from Mantissa) that was 
often praised by users.

Do you think we should design something now for 3.0 or should it wait 
4.0 ? I would love to have such a new feature soon, but fear it could 
delay 3.0 too much.

Luc

>
> Phil
>> Sebastien
>>
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>
>
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