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/******************************************************
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* Presage, an extensible predictive text entry system
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* ---------------------------------------------------
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* Copyright (C) 2008 Matteo Vescovi <matteo.vescovi@yahoo.co.uk>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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#ifndef PRESAGE_RECENCYPREDICTOR
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#define PRESAGE_RECENCYPREDICTOR
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#include "predictor.h"
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#include "../core/logger.h"
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#include "../core/dispatcher.h"
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/** Recency predictor, a recency promotion statistical predictor.
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* RecencyPredictor, based on recency promotion principle, generates
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* predictions by assigning exponentially decaying probability values
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* to previously encountered tokens. Tokens are assigned a probability
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* value that decays exponentially with their distance from the
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* current token, thereby promoting context recency
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* (from Wikipedia) A quantity is said to be subject to exponential
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* decay if it decreases at a rate proportional to its
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* value. Symbolically, this can be expressed as the following
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* differential equation, where N is the quantity and λ is a positive
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* number called the decay constant.
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* frac{dN}{dt} = -lambda N.
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* The solution to this equation is below:
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* N(t) = N_0 e^{-lambda t}
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* Here N(t) is the quantity at time t, and N0 = N(0) is the (initial)
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* quantity, at time t = 0.
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* This is the form of the equation that is most commonly used to
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* describe exponential decay. The constant of integration N0 denotes
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* the original quantity at t = 0. (The notation λ for the decay
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* constant is a remnant of the usual notation for an eigenvalue. In
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* this case, λ is the eigenvalue of the opposite of the
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* differentiation operator with N(t) as the corresponding
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class RecencyPredictor : public Predictor, public Observer {
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RecencyPredictor(Configuration*, ContextTracker*);
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virtual Prediction predict(const size_t size, const char** filter) const;
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virtual void learn(const std::vector<std::string>& change);
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virtual void update (const Observable* variable);
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void set_lambda (const std::string& value);
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void set_n_0 (const std::string& value);
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void set_cutoff_threshold (const std::string& value);
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static const char* LOGGER;
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static const char* LAMBDA;
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static const char* N_0;
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static const char* CUTOFF_THRESHOLD;
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size_t cutoff_threshold;
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Dispatcher<RecencyPredictor> dispatcher;
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#endif // PRESAGE_RECENCYPREDICTOR
added
removed
src/lib/predictors/recencyPredictor.h
