[Numpy-discussion] Matrix Class [was numpy release]

Robert Cimrman cimrman3@ntc.zcu...
Tue Apr 29 03:50:59 CDT 2008


Bill Spotz wrote:
> On Apr 28, 2008, at 10:47 PM, Bill Spotz wrote:
> 
>> As for this example, my version should work with a properly
>> implemented sparse_matrix A, but the array approach precludes that.
>> That is to say, I could convert A to a matrix if it is provided as an
>> array, but you could not convert a sparse_matrix to an array.
> 
> 
> I may be jumping to conclusions here.  We could conceivably implement  
> a sparse_array class upon which the sparse_matrix class is based.

FYI:
In scipy, the iterative solvers (cg and like) should work with 
LinearOperator (a class with matvec, rmatvec, and eventually matmat 
methods) passed instead of the A matrix argument. There is a function 
aslinearoperator() is scipy.sparse.linalg, that constructs a 
LinearOperator instance from a numpy array, matrix and scipy sparse 
matrix. It could be generalized to accept a function for a matrix-free 
computation, too. Also LinearOperator.__mul__, __rmul__ could be easily 
defined via matvec, rmatvec.

IMHO the all iterative solvers could use such a concept, to shield them 
from what the system matrix A or the preconditioner actually are and to 
be able writing them in a visually appealing way (i.e. close to what one 
writes on a paper).

regards,
r.


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