I was wondering why do you need to keep a = cst. ? Are you calibrating on a
> Hi all again,
>
> Is there a simpler way that doesn't modify the Vasicek implementation?
>
> In QL 0.3 I did a FixedAlphaHullWhite class, derived from HullWhite, which
> had a private member, derived from Optimization::Constraint::Impl, that was
> passing the correct parms to the optimization engines.
>
> I attach the old implementation of the class, which was working perfectly
> under QL0.3., oping that somebody has some good ideas about...
>
>
>
>
> 2010/4/22 Kim Kuen Tang <
[hidden email]>
>
> >
> > Hi Francesco,
> >
> > Francesco Perissin schrieb:
> >
> > Hi all,
> >> I need to calibrate the HullWhite model keeping fixed the a parameter.
> >> In order to do that, I think that I have to develop a FixedAlphaHullWhite
> >> class, derived from HullWhite, with a modification in the
> >> FittingParamater::Impl class, in order to
> >>
> > Vasicek is the class that you need to modify. The class FittingParamater is
> > there to fit the termstructure (yield curve). In the current implementation
> > a_ is initialized with arguments_[0], which is a member in the class model
> > (ql\models\model.hpp). This is how it tells quantlib that a_ is a
> > calibration parameter.
> >
> > Take a look at the constructor:
> >
> > Vasicek::Vasicek(Rate r0, Real a, Real b, Real sigma, Real lambda)
> > : OneFactorAffineModel(4), r0_(r0),
> > a_(arguments_[0]), b_(arguments_[1]), sigma_(arguments_[2]),
> > lambda_(arguments_[3]) {
> > a_ = ConstantParameter(a, PositiveConstraint());
> > b_ = ConstantParameter(b, NoConstraint());
> > sigma_ = ConstantParameter(sigma, PositiveConstraint());
> > lambda_ = ConstantParameter(lambda, NoConstraint());
> > }
> >
> > What you need to do, is to tell Vasicek that there are only three
> > parameters to calibrate , instead of four. Then you need to decouple a_
> from
> > the calibration process which is straightforward.
> >
> >
> > HTH
> >
> > Cheers
> > Kim
> >
> > have only sigma as fitting parameter, and erediting alpha from the
> >> FixedAlphaHullWhite class.
> >> I am not so keen in C++, so I have some trouble in doing this.
> >> Any suggestions?
> >> Many thanks
> >> Francesco
> >> ------------------------------------------------------------------------
> >>
> >>
> >>
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> >>
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> >>
> >
> >
>
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fixedalphahullwhite.hpp (2K)