[Dune-devel] Setting UMFPack parameters

[Oliver Sander]

Hi Dominic,

> its true that the interface of the UMFPack wrapper doesnt allow
> parameter tweaking. The main problem for me with it has been, that you
> definitely dont want to add methods for ALL umfpack options, as they
> are too many. This would result in an unreadable interface (most users
> wont care for those options anyway). I am surprised by the factor of 6
> you get out of there and that definitely means it should be
> considered.

Yeah, I was surprised by the factor 6, too.  From reading the documentation
I was expecting factor 3 maximum.  No idea why it is a factor 6.
Note that this is about back-substitution only.  It does not change
the factorization speed.


 I see two options:
> - Add methods to the Umfpack class for a subset of options, that we
> consider worthwile
> - add a method
> void setUMFParameter(int Parameter, double value)
> {
>   UMF_Control[Parameter] = value;
> }
> Such method would only be usable by a user that has studied the
> UMFPack Manual. I am in favor of this, as setting those parameters
> doesnt make much sense without being informed about what UMFPack does
> anyway.

I agree.  Such a method has now been added to the class.

Cheers,
Oliver


> Best,
> Dominic
> 
> 
> On Fri, Jan 17, 2014 at 11:48 AM, Oliver Sander
> <sander at igpm.rwth-aachen.de> wrote:
>> Hi Markus, hi Dominic, hi all,
>> I have been playing around with the ISTL-UMFPack wrapper recently.  As it turns out,
>> I can solve my problems six times faster without noticeable loss of accuracy by
>> switching off iterative refinement.  However there is no way to do that through the
>> interface.  More technically, I need to set values in the UMF_Control array.
>> Before I start hacking, do you have any specific ideas how an official way to modify
>> UMF_Control from the outside should look like?
>> Cheers,
>> Oliver
>>
>>
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