Estimate the minimum (double) value that the given function has in the interval [min,max] using Lambda. - Java Lambda Stream

Java examples for Lambda Stream:DoubleFunction

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Description

Estimate the minimum (double) value that the given function has in the interval [min,max] using Lambda.

Demo Code

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 * Copyright (c) 2013-2015 Marco Hutter - http://www.javagl.de
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//package com.java2s;
import java.util.ArrayList;
import java.util.List;
import java.util.function.DoubleFunction;

public class Main {
    /**
     * Estimate the minimum (double) value that the given function has in the
     * interval [min,max]. <br> 
     * <br>
     * If the function returns <code>null</code> or NaN for any value, this 
     * will be ignored. If the function returns <code>null</code> for all 
     * values, then <code>null</code> will be returned. If the function 
     * returns NaN for all values, then NaN will be returned.
     * 
     * @param min The minimum value
     * @param max The maximum value
     * @param function The function
     * @return The estimate for the minimum value
     */
    static Number estimateMinValue(
            DoubleFunction<? extends Number> function, double min,
            double max) {
        return computeMin(function, interpolate(min, max, 100));
    }

    /**
     * Compute the minimum (double) value of applying the given function to 
     * the given values.<br> 
     * <br>
     * If the function returns <code>null</code> or NaN for any value, this 
     * will be ignored. If the function returns <code>null</code> for all 
     * values, then <code>null</code> will be returned. If the function 
     * returns NaN for all values, then NaN will be returned.
     * 
     * @param function The function
     * @param values The values
     * @return The minimum
     */
    private static Number computeMin(
            DoubleFunction<? extends Number> function,
            Iterable<Double> values) {
        Number min = null;
        for (double x : values) {
            Number y = function.apply(x);
            min = min(min, y);
        }
        return min;
    }

    /**
     * Interpolate between the given minimum and maximum value (inclusive)
     * with the given number of steps and return the result as a list.
     * 
     * @param min The minimum value
     * @param max The maximum value
     * @param steps The number of steps
     * @return The list containing the interpolated values
     */
    static List<Double> interpolate(double min, double max, int steps) {
        List<Double> result = new ArrayList<Double>();
        for (int i = 0; i < steps; i++) {
            double alpha = (double) i / (steps + 1);
            double x = min + alpha * (max - min);
            result.add(x);
        }
        return result;
    }

    /**
     * Returns the minimum (double) of the given values.<br> 
     * <br>
     * If either value is <code>null</code>, then the other value will be 
     * returned. If both values are <code>null</code>, then <code>null</code>
     * will be returned. If neither value is <code>null</code>, and either 
     * value is NaN, then the other value will be returned. If both values 
     * are NaN, then NaN will be returned.
     * 
     * @param n0 The first value
     * @param n1 The second value 
     * @return The minimum
     */
    static Number min(Number n0, Number n1) {
        if (n0 == null) {
            return n1;
        }
        if (n1 == null) {
            return n0;
        }
        double d0 = n0.doubleValue();
        double d1 = n1.doubleValue();
        if (Double.isNaN(d0)) {
            return d1;
        }
        if (Double.isNaN(d1)) {
            return d0;
        }
        return Math.min(d0, d1);
    }
}

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