com.itemanalysis.psychometrics.statistics.NormalDensity.java Source code

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Here is the source code for com.itemanalysis.psychometrics.statistics.NormalDensity.java

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/*
 * Copyright 2012 J. Patrick Meyer
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.itemanalysis.psychometrics.statistics;

import org.apache.commons.math3.distribution.NormalDistribution;

/**
 *
 * @author J. Patrick Meyer
 */
@Deprecated
public class NormalDensity {

    private NormalDistribution normal = null;

    private double mean = 0.0;

    private double sd = 0.0;

    public NormalDensity(double mean, double sd) {
        normal = new NormalDistribution(mean, sd);
    }

    public NormalDensity() {
        normal = new NormalDistribution();
    }

    public double[][] value(int numPoints) {
        double min = mean - (3.5 * sd);
        double max = mean + (3.5 * sd);
        return value(min, max, numPoints);
    }

    public double[][] value(double min, double max, int numPoints) {
        numPoints = Math.max(1, numPoints);
        double[][] density = new double[numPoints][numPoints];
        double increment = (max - min) / (numPoints - 1);
        double val = min;
        double densitySum = 0.0;
        for (int i = 0; i < numPoints; i++) {
            density[i][0] = val;
            density[i][1] = normal.density(val);
            densitySum += density[i][1];
            val += increment;
        }

        //make sure probabilities sum to unity
        for (int i = 0; i < numPoints; i++) {
            density[i][1] = density[i][1] / densitySum;
        }

        return density;
    }

}