dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Thursday 05 March 2009 17:13:02 Garth N. Wells wrote:
> We have a high-level interface which provides operations like
>
>    A += B
>
> for matrices. 

For the record: This is not only for the python interface. The c++ operator+= 
also use axpy.

> This causes some problems as it hides the complexity which 
> is inherent in sparse matrices, in particularly with respect to whether
> or not the two matrices have the same non-zero pattern. Unless someone
> has a good idea as to get around this robustly, I suggest that we remove
> these functions for matrices. A user can still do
>
>      A.axpy(1.0, B)
>
> or
>
>      A.axpy(1.0, B, True)
>
> where the last argument indicates whether or not the sparsity patterns
> of A and B are the same (default is False).

A naive suggestion: 
Is it possible to compute a unique number based on our SparsityPattern? This 
number could be stored as a private member of a Matrix? Then only matrices 
from the same SparsityPattern will be addable. When ever a Matrix is changed, 
by other means than M.init(sp), this number will be set to some default 
incompatible number.

If we do not find a robust way to do this I am fine with removing the 
operators that use axpy, but I really think it is a neat feature which I 
would like to keep.

Johan