Step-15 uses a fixed alpha = 0.1, but in the suggestions it is proposed to
increase alpha to 1, when suitable in order to increase convergence. I am
also using a fixed alpha of 0.1 at the moment, thus it will never go to
zero.
Am Freitag, 6. Oktober 2017 15:27:40 UTC+2 schrieb Wolfgang Bangerth:
>
> On 10/06/2017 07:20 AM, 'Maxi Miller' via deal.II User Group wrote:
> > Isn't that basically the method done in step-15 and step-33 (line
> search)? But
> > why should my step length (I assume it is alpha) go to zero? Or is it
> the
> > newton-update (which also should go to zero, when being close to the
> solution)?
>
> The step length is alpha in
>
> u_{n+1} = u_n + alpha delta u_n
>
> I don't think step-15 uses a line search (i.e., it *always* uses alpha=1).
> I
> don't recall about step-33.
>
> Your question "why should my step length (I assume it is alpha) go to
> zero?"
> Is the wrong one. Maybe it shouldn't. The question is whether it does.
> Debugging is all about understanding that what you *think is true* is
> apparently not true. So you have to test hypotheses.
>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: bang...@colostate.edu
> <javascript:>
> www: http://www.math.colostate.edu/~bangerth/
>
>
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