dolfin team mailing list archive

[Johan Jansson <johanjan@xxxxxxxxxxxxxxxx>]

On Fri, Aug 11, 2006 at 02:42:49PM +0200, Anders Logg wrote:
> Could we define a GenericMatrixElement in the same way as we have
> defined a PETScMatrixElement to allow access according to
> 
>     a = A(i, j)
>     A(i, j) = a
> 
> ?
> 
> This will be *slow* for PETSc, but fast for uBlas. The question is if
> we can do this without introducing any overhead when indexing a
> matrix that is known to be a uBlasMatrix at compile-time.
> 
> /Anders

I don't like this kind of workaround (i.e. MatrixElement,
VectorElement) for just defining an operator. Here's my suggestion:

Let's define functions getelement()/setelement() for GenericVector and
GenericMatrix. The implementation for PETSc will be slow but for dense
uBlas very fast.

We can then define nice operators in Python for these functions with
__getitem__()/__setitem__():

    def __setitem__(self, i, a):
        if(isinstance(i, int)):
            self.setelement(i, a)
        elif(isinstance(i, tuple)):
            self.setelement(i[0], i[1], a)

In C++, the uBlas indexing interface already exists, so we can use that.

What do you think?

  Johan