[petsc-users] default orthogonalization in gmres

[Umut Tabak]

On 07/15/2013 08:54 PM, Matthew Knepley wrote:
>
>
> On Jul 15, 2013 1:51 PM, "Umut Tabak" <u.tabak at tudelft.nl 
> <mailto:u.tabak at tudelft.nl>> wrote:
> >
> > Hi list,
> >
> > I was wondering the reason why classical gram schmidt is used in the 
> orthogonalizations in the gmres implementation as default? As far as I 
> remember, this was unstable numerically.
>
Hi Matt,

Excuse my naive question but mathematically they are equivalent so what 
is the source of speed boost? And can you please direct me to one or two 
of these references?

Best,
Umut
>
> Its much faster. Try the modified option and compare. There are many 
> papers claiming that classical+selective reorthogonalization is just 
> as stable.
>
>    Matt
> >
> > Best,
> > Umut
>

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