com.gedaeusp.domain.ExponentialParametric.java Source code

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Here is the source code for com.gedaeusp.domain.ExponentialParametric.java

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/*
Copyright 2014 Antnio Miranda, Caio Valente, Igor Topcin, Jorge Melegati, Thales Paiva, Victor Santos
    
This file is part of PhysUSP.
    
PhysUSP 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.
    
PhysUSP 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 PhysUSP. If not, see <http://www.gnu.org/licenses/>.
*/

package com.gedaeusp.domain;

import org.apache.commons.math3.analysis.ParametricUnivariateFunction;
import org.apache.commons.math3.util.FastMath;

public class ExponentialParametric implements ParametricUnivariateFunction {

    private boolean fixedV0;

    public ExponentialParametric() {
        this(false);
    }

    public ExponentialParametric(boolean fixedV0) {
        this.fixedV0 = fixedV0;
    }

    @Override
    public double value(double t, double... params) {
        double v0 = params[Exponential.PARAM_v0];
        double a = params[Exponential.PARAM_a];
        double tau = params[Exponential.PARAM_tau];

        return Exponential.value(t, v0, a, tau);
    }

    @Override
    public double[] gradient(double t, double... params) {
        double a = params[Exponential.PARAM_a];
        double tau = params[Exponential.PARAM_tau];

        double dv0 = fixedV0 == true ? 0 : 1;
        double da = FastMath.exp(-t / tau);
        double dTau = a * t * FastMath.exp(-t / tau) / FastMath.pow(tau, 2);

        return new double[] { dv0, da, dTau };
    }

}