dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, May 08, 2009 at 08:12:35AM +0200, Johan Hake wrote:
> On Thursday 07 May 2009 23:16:54 Anders Logg wrote:
> > On Thu, May 07, 2009 at 11:05:49PM +0200, Johan Hake wrote:
> > > On Thursday 07 May 2009 18:54:04 Anders Logg wrote:
> > > > I've added some of the requested features to the parameter system,
> > > > some pushed and some sitting here in a local repository. But the
> > > > current design makes it a pain to add new features. A single change
> > > > will make it necessary to add a function in at least 5 different
> > > > classes.
> > > >
> > > > So I'm thinking of reimplementing and simplifying the parameter
> > > > system. I think I know how to make it simpler.
> > > >
> > > > But before I do that, does anyone have opinions on the
> > > > design/implementation? Is there any third-party library that we
> > > > could/should use (maybe something in boost)?
> > >
> > > It would be nice to have something that easely could be transferable to
> > > Python.
> > >
> > > Having a base class let say Parameterized and then let all inherit this
> > > to be able to define parameters will not work well for the shared_ptr
> > > interface we have. We have problems with the Variable class, which does
> > > not work for the derived shared_ptr classes e.g. Function. I would rather
> > > have classes that have a parameter rather than beeing.
> >
> > How would that work? Inheritance now provides get/set functions for
> > subclasses making it possible to do
> >
> >   solver.set("tolerance", 0.1);
> 
> Not sure what you ask for here. I know of Parametrized and I agree that the 
> above syntax is nice. But I prefer to keep the parameters in its own object 
> and just operate on that. These can then be collected into one "dict/map" and 
> then form the parameters of an application. This is also easier to wrap to 
> python. 
> 
> The shared_ptr argument might not be so relevant as the potential parametrized 
> classes may not be declared as shared_ptr classes in the swig interface 
> anyway. However if that will be the case we must declare Parametrized as a 
> shared_ptr class in swig and then we must declare all Parametrized sub 
> classes as shared_ptr... 
> 
> > > Also by defining a parameter(list/dict) class which can be accessed as a
> > > dict let us make the transition to python smoother.
> > >
> > >    ParameterDict p = solver.default_params();
> > >    p["abs_tol"] = 1e-9;
> >
> > It would need to be
> >
> >     ParameterDict& p = solver.default_params();
> 
> Sure :P
> 
> > and I'd suggest naming it Parameters:
> >
> >     Parameters& p = solver.parameters();
> 
> Fine.
> 
> > > By defining some templated check classes we could controll the
> > > assignment. In the Solver:
> > >    ...
> > >    ParameterDict& default_params(){
> > >       if (!_par)
> > >       {
> > >          _par = new ParameterDict();
> > >          _par->add_param("abs_tol",new RangeCheck<double>(1e-15,0,1));
> > >          vector<string> * allowed_prec = new Vector<string>();
> > >          allowed_prec->push_back("ilu");
> > >          allowed_prec->push_back("amg");
> > >          allowed_prec->push_back("jacobi");
> > >          _par->add_param("prec",new
> > > OptionCheck<string>("ilu"),allowed_prec));
> > > _par->add_param("nonsense","jada"); // No checks
> > >       }
> > >    }
> > >
> > > Well, I admit that the above code is not beautiful, and others can
> > > probably make it cleaner and spot errors. The point is that RangeCheck
> > > and OptionCheck can be derived from a ParCheck class that overloads the
> > > operator=(). This will just call a private set function which is defined
> > > in the derived classes, and which do the check.
> >
> > I think we can also solve this without excessive templating... ;-)
> 
> Good!
> 
> > > The to and from file can be implemented in the ParameterDict body. The
> > > checks do not have to be written or read, as a ParameterDict can only
> > > read in allready predefined parameters, and the check will be done when
> > > the file is read.
> > >
> > > The option parser ability can also be implemented in ParameterDict using
> > > boost or other libraries, based on the registered parameters.
> > >
> > > I have implemented something like this in Python, and the above is a try
> > > to scetch something similare in c++.
> >
> > What exactly is needed from the Python side? I think I can make a
> > fairly simple implementation of this in C++ using a minimal amount of
> > templates with simple syntax.
> 
> Using operator[] to get and set parameters can straightforwardly be mapped to 
> python, and we can then also implement the map/dict protocol on top of that. 
> Other get and set methods can also be used, however set is a built in type in 
> Python and not a good alternative.
> 
> > Is the main difference that instead of inheriting Parametrized, a
> > subclass needs to implement a method named parameters() which returns
> > the parameter "dictionary"?
> 
> Yes. 

ok, I'll try this. I'll add a sketch of a new class using as much of
po as seems reasonable and then you could have a look before I proceed.

-- 
Anders

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