dolfin team mailing list archive

[N <tenpoundwalleye@xxxxxxxxx>]

----- Original Message ----
> From: Johan Hake <hake@xxxxxxxxx>
> To: dolfin-dev@xxxxxxxxxx
> Cc: N <tenpoundwalleye@xxxxxxxxx>
> Sent: Tuesday, February 17, 2009 4:42:46 PM
> Subject: Re: [DOLFIN-dev] access to CSR data in python
> 
> On Monday 16 February 2009 23:29:48 N wrote:
> > Take a simple example like
> >
> > from dolfin import *
> > mesh = UnitSquare(4, 4)
> > V = FunctionSpace(mesh, "CG", 1)
> > v = TestFunction(V)
> > u = TrialFunction(V)
> > a = dot(grad(v), grad(u))*dx
> > A = assemble(a)
> >
> > The matrix A (with boost as the linear algebra base) gives the following
> > for attribute data: data(self) ->
> > std::tr1::tuple<(p.q(const).std::size_t,p.q(const).std::size_t,p.q(const).d
> >ouble,int)>
> >
> >     Return pointers to underlying compressed storage data. See
> >     GenericMatrix for documentation.
> >
> >
> > How can this be used to gain access to the column data, row pointer, and
> > data elements in the matrix?  I would like to have access to this data in
> > Numpy arrays without copying the data.  Is this possible?
> 
> You now can. Sorry that I did not made it to the release ;)
> 
> You can now do:
> 
>   >>> rows, cols, values = A.data()
> 
> Here rows, cols and values are numpy arrays based on pointers to the 
> underlaying data structures in c++.
> 
> It works for the linear algebra backends that supports the feature in C++, 
> uBLAS and MTL4. Error is raised for the other backends.
> 
> Also added direct access to Vector data through the same data() function:
> 
>   >>> values = v.data()
> 
> This is similare to v.array(), but with no copying. This feature is also only 
> supported for the uBLAS and MTL4 backends.
> 

Perfect.  Works well.

I'm curious how implemented this.  I worked long and hard with both swig and direct python extensions to no avail.  Can you point me to your changes?

Thanks,
Nate