dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

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. 

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;

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.

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++.


Johan