Hi Thomas,
great, it works that way! Thank you very much! It is nice that I don't
have to do the derivation myself anymore! Is there any perfomance
drawback if the derivation is done internally?
Best regards,
Franz
Am Mittwoch, den 22.05.2013, 14:51 +0200 schrieb Thomas Neidhart:
> Hi Franz,
>
> you can take a look at the following class which is used for the unit tests:
>
> public class QuinticFunction implements UnivariateDifferentiableFunction {
>
> /* Evaluate quintic.
> * @see org.apache.commons.math3.UnivariateFunction#value(double)
> */
> public double value(double x) {
> return (x-1)*(x-0.5)*x*(x+0.5)*(x+1);
> }
>
> public DerivativeStructure value(DerivativeStructure t) {
> return
> t.subtract(1).multiply(t.subtract(0.5)).multiply(t).multiply(t.add(0.5)).multiply(t.add(1));
> }
>
> }
>
> The DerivativeStructure provides the standard arithmetic operations which
> you can use.
> So in your case the value method would look like this imho:
>
> public DerivativeStructure value(DerivativeStructure t) {
> return t.multiply(t);
> }
>
> This just a quick help from myside, Luc (Maisonobe) will surely give you
> more infos on how to use the DerivativeStructure.
>
> Thomas
>
>
>
> On Tue, May 21, 2013 at 4:21 PM, Franz Simons <
> [email protected]> wrote:
>
> > Dear all,
> >
> > I don't understand the usage of the new DerivativeStructure in version 3
> > of the commons math.
> >
> > In the old version I had the following function, which was then used in
> > the Newton solver:
> >
> > public class MyFunction implements
> > DifferentiableUnivariateRealFunction {
> >
> >
> > public double value(double x) {
> > // example value
> > return x*x;
> > }
> >
> > public UnivariateRealFunction derivative() {
> > return new UnivariateRealFunction() {
> > public double value(double x) {
> > // example derivative
> > return 2.*x;
> > }
> > }
> > }
> > }
> >
> > To use the Newton Raphson solver in version 3, I have to implement the
> > new UnivariateDifferentiableFunction interface:
> >
> > public class MyFunctionNew implements
> > UnivariateDifferentiableFunction {
> >
> > public double value(double x) {
> > // example value
> > return x*x;
> > }
> >
> > public DerivativeStructure value(DerivativeStructure t) {
> >
> > // What do I have to do here??
> > // return what?
> > }
> > }
> >
> > I don't know how to use the DerivativeStructure. What do I have to do,
> > to get the same functionality like in the the previous function? How can
> > I define the derivative of my function?
> > I tried to understand from the user guide, but it wasn't clear for me.
> >
> > It would be great if someone could give me a hint or further explanation
> > on this.
> >
> > Thank you very much in advance!
> >
> > Best regards,
> > Franz
> >
> >
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> > For additional commands, e-mail: [email protected]
> >
> >
--
Dipl.-Ing. Franz Simons
Fachgebiet Wasserwirtschaft und Hydrosystemmodellierung
Chair of Water Resources Management and Modeling of Hydrosystems
Institut für Bauingenieurwesen
Technische Universität Berlin | Sekr. TIB 1-B14
Gustav-Meyer-Allee 25 | 13355 Berlin | Germany
Tel.: +49 30 314-72429 | Fax: +49 30 314-72430
[email protected] | www.wahyd.tu-berlin.de
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