[petsc-users] Yet another inversion question

[Umut Tabak]

Jed Brown wrote:
> You say that both A and B are sparse, what are you going to do with the
> product C = A^{-1} B?  The most common thing is to apply it to some
> vectors or perhaps compute a few eigen/singular values/vectors.  You
> rarely need an explicit representation of the product to do such things.
>
>   
Dear Barry and Jed,

Thanks for the swift replies.

Barry,

that goes really slower than what I tried. That is not the way to go I 
suppose.

Jed,

I have some kind of a symmetrization(or call transformation) matrix for 
symmetrizing an unsymmetric problem. I need these terms in this explicit 
symmetrization matrix. I guess this is also a rare case. I could not 
device an analytical expression to get rid of these kinds of terms yet. 
That is why I try different approaches, not with high expectations though.
> It is extremely unlikely that C is symmetric.
>
>   
Yep, you are right ;)
> This will work, you could also use the lower level interface to factor
> A, MatConvert() B to MATDENSE, then MatMatSolve() the result.
> Internally this will do something very similar to what you have already
> done, it's questionable whether it would actually be faster (it will
> certainly use more memory).
>   
I will see what this does.

Thanks and best,
Umut