[petsc-users] How to efficiently represent a diagonal matrix?

[Jed Brown]

Fande Kong <fdkong.jd at gmail.com> writes:

> On Wed, Feb 14, 2018 at 4:35 PM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
>
>>
>>   What are you doing with the matrix?
>>
>
> We are doing an explicit method. PDEs are discretized using a finite
> element method, so there is a mass matrix. The mass matrix will be lumped,
> and it becomes diagonal. We want to compute the inverse of the lumped
> matrix, and also do a few of matrix-vector multiplications using  the
> lumped matrix or  its inverse.
>
> The specific implementation won't make this more efficient?

You can use pretty much any representation and you won't notice the time
because you still have to apply the RHS operator and that is vastly more
expensive.