FittedBondDiscountCurve::FittingMethod Class Referenceabstract

Base fitting method used to construct a fitted bond discount curve. More...

`#include <ql/termstructures/yield/fittedbonddiscountcurve.hpp>`

Inheritance diagram for FittedBondDiscountCurve::FittingMethod:
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## Public Member Functions

virtual Size | size () const =0
| total number of coefficients to fit/solve for
Array | solution () const
| output array of results of optimization problem
Integer | numberOfIterations () const
| final number of iterations used in the optimization problem
Real | minimumCostValue () const
| final value of cost function after optimization
virtual std::auto_ptr< FittingMethod > | clone () const =0
| clone of the current object
bool | constrainAtZero () const
| return whether there is a constraint at zero
Array | weights () const
| return weights being used
Array | l2 () const
| return l2 penalties being used
ext::shared_ptr< OptimizationMethod > | optimizationMethod () const
| return optimization method being used
DiscountFactor | discount (const Array &x, Time t) const
| open discountFunction to public

## Protected Member Functions

| FittingMethod (bool constrainAtZero=true, const Array &weights=Array(), const ext::shared_ptr< OptimizationMethod > &optimizationMethod=ext::shared_ptr< OptimizationMethod >(), const Array &l2=Array(), Real minCutoffTime=0.0, Real maxCutoffTime=QL_MAX_REAL)
| constructors
virtual void | init ()
| rerun every time instruments/referenceDate changes
virtual DiscountFactor | discountFunction (const Array &x, Time t) const =0
| discount function called by FittedBondDiscountCurve

## Protected Attributes

bool | constrainAtZero_
| constrains discount function to unity at \( T=0 \), if true
FittedBondDiscountCurve * | curve_
| internal reference to the FittedBondDiscountCurve instance
Array | solution_
| solution array found from optimization, set in calculate()
Array | guessSolution_
| optional guess solution to be passed into constructor. More...
ext::shared_ptr< FittingCost > | costFunction_
| base class sets this cost function used in the optimization routine

## Friends

class | FittedBondDiscountCurve

## Detailed Description

Base fitting method used to construct a fitted bond discount curve.

This base class provides the specific methodology/strategy used to construct a FittedBondDiscountCurve. Derived classes need only define the virtual function discountFunction() based on the particular fitting method to be implemented, as well as size(), the number of variables to be solved for/optimized. The generic fitting methodology implemented here can be termed nonlinear, in contrast to (typically faster, computationally) linear fitting method.

Optional parameters for FittingMethod include an Array of weights, which will be used as weights to each bond. If not given or empty, then the bonds will be weighted by inverse duration

An optional Array may be provided as an L2 regularizor in this case a L2 (gaussian) penalty is applied to each parameter starting from the initial guess. This is the same as giving a Gaussian prior on the parameters

\[ d(t) = \sum_{i=0} c_i b_i(t) \]

i.e., linear in the unknown coefficients \( c_i \). Such a fitting can be reduced to a linear algebra problem \( Ax = b \), and for large numbers of bonds, would typically be much faster computationally than the generic non-linear fitting method.

Warning:
  some parameters to the Simplex optimization method may need to be tweaked internally to the class, depending on the fitting method used, in order to get proper/reasonable/faster convergence.

## Member Data Documentation

## guessSolution_

Array guessSolution_

protected

optional guess solution to be passed into constructor.

The idea is to use a previous solution as a guess solution to the discount curve, in an attempt to speed up calculations.