[petsc-users] snes linesearch bt vs basic?

Matthew Knepley knepley at gmail.com
Mon Feb 1 13:59:40 CST 2016

On Mon, Feb 1, 2016 at 1:46 PM, Xiangdong <epscodes at gmail.com> wrote:

> Hello everyone,
> I have a question on snes with line search. Under what circumstance,
> applying the (globalized) line search can perform WORSE than without line
> search (i.e. full newton step ls type basic)?
> When I apply snes with my problem, I found that at some time steps, snes
> diverges with linesearch_bt, but can converge with linesearch_basic (using
> same initial guess). For the same problem, there are also some steps, at
> which linearsearch_basic fails, but linesearch_bt converges. Is there a
> general guide line to decide whether linesearch should be used?

No, and it is likely impossible to give one. 'basic' can succeed by taking
some non-decreasing steps which happen to fall into
a basin of convergence, whereas 'bt' will succeed in many circumstances
where basic diverges. If we knew how to do this,
we could retire.


> Thanks.
> Xiangdong

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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