travelTimesBack.PbackODE.java Source code

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Here is the source code for travelTimesBack.PbackODE.java

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/*
 * GNU GPL v3 License
 *
 * Copyright 2015 Marialaura Bancheri
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package travelTimesBack;

import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.ode.FirstOrderDifferentialEquations;

// TODO: Auto-generated Javadoc
/**
 * The Class PbackODE implements the first order differential equation 
 * for the computation of the residence time pdf, given the water storage,
 * the discharge and AET. Omega_Q and omega_ET are the values of the 
 * storage selection functions. The output is p_back(t-ti|ti). 
 */
public class PbackODE implements FirstOrderDifferentialEquations {

    public double S_t;

    public double S_t1;

    public double Q;

    public double ET;

    public double omega_Q;

    public double omega_ET;

    public double p_back;

    public double dt;

    /**
     * Instantiates the first order differential equation for the
     * the computation of p_back.
     *
     * @param S_t: the water storage at time t
     * @param S_t1: the water storage at time t+1
     * @param Q: the discharge
     * @param ET: the AET
     * @param omega_Q: the SAS for the discharge
     * @param omega_ET:the SAS for the ET
     * @param p_back: backward probability at time t-1
     * @param dt: integration time
     */
    public PbackODE(double S_t, double S_t1, double Q, double ET, double omega_Q, double omega_ET, double p_back,
            double dt) {
        this.S_t = S_t;
        this.S_t1 = S_t1;
        this.Q = Q;
        this.ET = ET;
        this.omega_Q = omega_Q;
        this.omega_ET = omega_ET;
        this.p_back = p_back;
        this.dt = dt;
    }

    /* (non-Javadoc)
     * @see org.apache.commons.math3.ode.FirstOrderDifferentialEquations#getDimension()
     */
    public int getDimension() {
        return 2;
    }

    /* (non-Javadoc)
     * @see org.apache.commons.math3.ode.FirstOrderDifferentialEquations#computeDerivatives(double, double[], double[])
     */
    public void computeDerivatives(double t, double[] y, double[] yDot)
            throws MaxCountExceededException, DimensionMismatchException {
        yDot[0] = 1 / S_t1 * (-Q * omega_Q - ET * omega_ET) * y[0] - (S_t1 - S_t) * y[0] / S_t1;

    }

}