how efficient is the block diagonal format?

[Barry Smith]

   Alejandro,

    I would be surprised if either format was particularly much
better than the other. 

   Barry

On Thu, 30 Aug 2007, Alejandro Garzon wrote:

> 
> Hi, first of all thanks for your previous help. In section 3.1.1 of the user's
> manual it is said "Additional formats (such as block compressed row and block
> diagonal storage, which are generally much more efficient for problems with
> multiple degrees of freedom per node) are discussed below." I want to know if
> the efficiency refers to the assembly only or if more important it refers also
> to how the KSPSolve function will perform with this format. I did a trial and it
> seems KSPSolve performs at around the same speed with both the default and the
> block diagonal formats (is even a bit faster with the default format). Is this
> comparison highly problem dependent? Or could I be missing to use some option?
> My problem is a 1D pde with 2 variables (two degrees of freedom per node(?))
> first and second derivatives terms and a block on the main diagonal mixing the
> two variables. Thanks.
> 
> Alejandro.
> 
>