Creating a new bias-corrector
A bias-correction scheme adjusts forecasts. The adjustment model has parameters that are estimated based on past data. The developer must write two functions:
correct and
updateParameters
1 class Corrector : public Component {
2 public:
3 Corrector(const Options& iOptions, const Data& iData);
4
5 void correct(const Parameters& iParameters, Ensemble& iEnsemble) const;
6 void updateParameters(const std::vector<Ensemble>& iUnCorrected,
7 const std::vector<Obs>& iObs,
8 Parameters& iParameters) const;
9 void getDefaultParameters(Parameters& iParameters) const;
10
11 static Corrector* getScheme(const Options& rOptions, const Data& iData);
12 static Corrector* getScheme(const std::string& iTag, const Data& iData);
13 virtual bool isMemberSpecific() const;
14 //! Does this method need the input ensemble to be the same size everytime?
15 //! E.g. for parameter estimation
16 bool needsConstantEnsembleSize() const;
17 protected:
18 virtual void correctCore(const Parameters& iParameters, Ensemble& iEnsemble) const = 0;
19 virtual void getDefaultParametersCore(Parameters& iParameters) const {};
20 //! Default: Don't update
21 //! Guarantee: Number of ensembles and obs are the same
22 virtual void updateParametersCore(const std::vector<Ensemble>& iUnCorrected,
23 const std::vector<Obs>& iObs,
24 Parameters& iParameters) const {};
25 bool mMemberSpecific; ///< Does correction apply to each ensemble member separately?
26 bool mPoolParameters; ///< Are the same parameters used on different members?
27 bool mEnforceLimits; ///< Should corrected value be forced to be within variables limits?
28 private:
29 void enforceLimits(Ensemble& iEnsemble) const;
30 }
The header file
$COMPS/src/Correctors/New.h will contain:
1 class CorrectorNew : public Corrector {
2 public:
3 CorrectorNew(const Options& iOptions, const Data& iData);
4 bool isMemberSpecific() const;
5 protected:
6 void correctCore(const Parameters& iParameters, Ensemble& iEnsemble) const;
7 void getDefaultParametersCore(Parameters& iParameters) const;
8 void updateParametersCore(const std::vector<Ensemble>& iUnCorrected,
9 const std::vector<Obs>& iObs,
10 Parameters& iParameters) const;
11 }
The implementation file
$COMPS/src/Correctors/New.cpp will contain:
1 // Specifies how to correct an ensemble given a set of parameters
2 void CorrectorNew::correctCore(const Parameters& iParameters, Ensemble& iEnsemble) const {
3 float correction = iParameters[0];
4
5 // Correct each ensemble member
6 for(int i = 0; i < iEnsemble.size(); i++) {
7 // ... but only if the member is not missing
8 if(Global::isValid(iEnsemble[i])) {
9 iEnsemble[i] = iEnsemble[i] + correction;
10 }
11 }
12 }
13
14 // Specifies how old parameters should be updated based on new information
15 void CorrectorNew::updateParametersCore(const Ensemble& iUnCorrected, const std::vector<Obs>& iObs,
16 Parameters& iParameters) const {
17 float ensMean = iUnCorrected.getMoment(1);
18 float error = iObs.getValue() - ensMean;
19 // Weighted average of the old parameter with the new evidence
20 iParameters[0] = combine(iParameters[0], error);
21 }