[SciPy-dev] Updated generic optimizers proposal
Wed Apr 25 06:33:20 CDT 2007
I have been accepted for participating in the GSoC program with project
related to scipy and optimization.
If noone else here is able or have no time, I would take a look
(however, I can't spend much time before summer start because of my
exams; and anneal (as well as other global solvers) is not my specialty).
I think that lb-ub bounds can hardly be implemented in a simple way
because it depends very much on rand points generator quality, and the
latter should be much more better than simple lb+rand*(ub-lb) elseware
all points will be located in a thin area near their average value (same
problem is present in integration of functions f: R^n->R with high
dimensions (n>>1) ).
I took a look at the generators by Joachim Vandekerckhove in his anneal
(connected to my openopt for MATLAB/Octave), they seems to be too primitive.
BTW afaik anneal currenlty is concerned as deprecated (I don't know
better English word, not "up-to-date", old one), there are better global
solvers, for example GRASP-based.
william ratcliff wrote:
> say, who's responsible for the anneal portion of optimize? I'd like
> to check in a minor tweak which implements simple upper and bounds on
> the fit parameters.
> On 4/18/07, *Matthieu Brucher* <firstname.lastname@example.org
> <mailto:email@example.com>> wrote:
> I'm lauching a new thread, the last was pretty big, and as I
> almost put every advice in this proposal, I thought it would be
> First, I used scipy coding standard, I hope I didn't forget
> I do not know where it would be put at the moment on my scipy
> tree, and the tests are visual for the moment, I have to make them
> automatic, but I do not know the framework used by scipy, I have
> to check it first.
> So, the proposal :
> - combining several objects to make an optimizer
> - a function should be an object defining the __call__ method and
> graient, hessian, ... if needed. It can be passed as several
> separate functions as Alan suggested it, a new object is then created
> - an optimizer is a combination of a function, a step_kind, a
> line_search, a criterion and a starting point x0.
> - the result of the optimization is return after a call to the
> optimize() method
> - every object (step or line_search) saves its modification in a
> state variable in the optimizer. This variable can be accessed if
> needed after the optimization.
> - after each iteration, a record function is called with this
> state variable - it is a dict, BTW -, if you want to save the
> whole dict, don't forget to copy it, as it is modified during the
> For the moment are implemented :
> - a standard algorithm, only calls step_kind then line_search for
> a new candidate - the next optimizer would be one that calls a
> modifying function on the computed result, that can be useful in
> some cases -
> - criteria :
> - monotony criterion : the cost is decreasing - a factor can be
> used to allow an error -
> - relative value criterion : the relative value error is higher
> than a fixed error
> - absolute value criterion : the same with the absolute error
> - step :
> - gradient step
> - Newton step
> - Fletcher-Reeves conjugate gradient step - other conjugate
> gradient will be available -
> - line search :
> - no line search, just take the step
> - damped search, it's an inexact line search, that searches in
> the step direction a set of parameters than decreases the cost by
> dividing by two the step size while the cost is not decreasing
> - Golden section search
> - Fibonacci search
> I'm not pulling other criterion, step or line search, as my time
> is finite when doing a structural change.
> There are 3 classic optimization test functions in the package,
> Rosenbrock, Powell and a quadratic function, feel free to try
> them. Sometimes, the optimizer converges to the true minimum,
> sometimes it does not, I tried to propose several solutions to
> show that every combinaison does not manage to find the minimum.
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