[petsc-dev] Line search

Mark Adams mfadams at lbl.gov
Wed Feb 15 14:09:07 CST 2017

> > Its not a coincidence that it is equal to the FunctionEval time. That is
> the main cost.
>    Mark,
>     When Newton is in the quadratic basin then it will do one Function
> evaluation and one Jacobian evaluation per Newton step. The one function
> evaluation takes place inside the line search code (and the result is used
> also at the beginning of the next iteration). If Newton is not in the
> quadratic basin it may do several function evaluations inside the line
> search (to find a suitable decrease in the function norm); again basically
> all the work in the line search is the function evaluations, there is
> nothing else computationally expensive in a line search (maybe a
> matrix-vector product).
Barry, I am trying to understand what is going on in the code. First,
someone is writing a paper with me and says we use 'line search', but they
do not (they specify 'basic'), and I wanted to get it straight. Second,
another project has expensive function evaluation, same cost as a Jacobian,
it is an unusual model. I know I am not doing extra function evaluations (I
would notice that), but I just want to make sure I understand exactly what
the code is doing and that I have my nomenclature straight (I have never
thought much about line search).

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