Re: [Dclib-devel] Root-finding algorithm in DLib

[Davis K. <dav...@us...>]

Well, to describe find_min_single_variable() in terms of what is
described on wikipedia
(http://en.wikipedia.org/wiki/Root-finding_algorithm),
find_min_single_variable() first finds a bracket containing the
minimizer and then uses interpolation to shrink the bracket to the
solution.  So it's pretty representative of general purpose root
finding methods that don't require the user to supply a derivative.
So it sounds like a reasonable thing to use for your problem.  In your
case, you just have to ask it to minimize f(r)^2 so that the root is
the minimum and it should work fine.

Cheers,
Davis

On Sat, May 31, 2014 at 12:48 PM, Zhoulai <ze...@gm...> wrote:
> Hello,
>
> I am new to Dlib,  but I am surprised that  there is no root-finding
> procedures in Dlib. Although  the functionality provided by the
> optmization.h should also be able to solve root-finding problems, I guess
> that comes with a higher complexity?
>
> So what if I want to solve a problem as follows using Dlib?
>
> I have a one dimensional function 'f' which is not necessarily
> differentiable. I want to find a root 'r' that is closest  to an initial
> guess 'g' so that f(r)=0 ?
>
> More formally, I am looking for a low-cost way to  minimize |r-g|
> under the constraint f(r)=0;
>
> In my problem setting, it is likely the initial guess is the root, thus I
> would use 'g' as an initial guess. However, I do not have an interval [a,b]
> such that f(a).f(b)<0 which is a common request for most root-finding
> procedures.
>
> Of course the problem above can be handled by the optimization approaches
> like find_min_single_variable etc, but my guess is that it can also treated
> as a root-finding problem which is less expensive.  What do you think?
>
> Thank you for your ideas.
>
> Sncerely,
> Zhoulai
>
>
>
>
>
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