Polynomial.java

/*
    BeepBeep, an event stream processor
    Copyright (C) 2008-2018 Sylvain Hallé

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package functions;

import ca.uqac.lif.cep.functions.StreamVariable;
import ca.uqac.lif.cep.functions.Constant;
import ca.uqac.lif.cep.functions.Function;
import ca.uqac.lif.cep.functions.FunctionException;
import ca.uqac.lif.cep.functions.FunctionTree;
import ca.uqac.lif.cep.functions.PassthroughFunction;
import ca.uqac.lif.cep.util.Numbers;

/**
 * Use an {@link StreamVariable} and a {@link FunctionTree} to create
 * the polynomial function <i>x</i><sup>2</sup>+3.
 * 
 * @author Sylvain Hallé
 */
public class Polynomial extends PassthroughFunction
{
    /*
     * We need to implement the getFunction() method, which must
     * return an object of type Function. Here, we create a FunctionTree
     * that computes x^2+3.
     */
    @Override
    public Function getFunction()
    {
        /* At the top level, the polynomial is an addition of two
         * terms. Hence the top of the function tree is the function
         * Addition, followed by two arguments. */
        return new FunctionTree(Numbers.addition,
                /* The first argument is itself a FunctionTree that computes
                 * the square of the argument. */
                new FunctionTree(Numbers.power,
                    /* This is done by using the Power function. StreamVariable.X
                     * refers by default to the first argument passed to a function. */
                    StreamVariable.X,
                    new Constant(2)),
                /* The second term of the addition is the constant 3 */
                new Constant(3));
    }

    /*
     * Small main() to illustrate the concept
     */
    public static void main(String[] args) throws FunctionException
    {
        Polynomial poly = new Polynomial();
        Object[] value = new Object[1];
        poly.evaluate(new Integer[]{3}, value);
        System.out.printf("Return value of the function: %f\n", value[0]);
        poly.evaluate(new Integer[]{8}, value);
        System.out.printf("Return value of the function: %f\n", value[0]);
    }
}