Example usage for org.apache.commons.math.distribution NormalDistributionImpl NormalDistributionImpl

Introduction

In this page you can find the example usage for org.apache.commons.math.distribution NormalDistributionImpl NormalDistributionImpl.

Prototype

public NormalDistributionImpl(double mean, double sd, double inverseCumAccuracy) 

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Document

Create a normal distribution using the given mean, standard deviation and inverse cumulative distribution accuracy.

Usage

From source file:org.smurn.jsift.GaussianFilter.java

/**
 * Builds a one dimensional gaussian kernel.
 * @param sigma Standard deviation of the kernel.
 * @return Discretized kernel. Array length is odd, kernel is centered.
 */// www  . j  av a2s  .c  o  m
private static double[] buildKernel(final double sigma) {

    int windowSize = (int) Math.ceil(WINDOW_SIZE_FACTOR * sigma);

    NormalDistributionImpl ndist = new NormalDistributionImpl(0.0, sigma, PRECISION);

    double[] kernel = new double[2 * windowSize + 1];
    double sum = 0;
    try {
        for (int i = 0; i < kernel.length; i++) {
            double x = i - windowSize;
            kernel[i] = ndist.cumulativeProbability(x - 0.5, x + 0.5);
            sum += kernel[i];
        }
    } catch (MathException ex) {
        throw new RuntimeException(ex);
    }
    for (int i = 0; i < kernel.length; i++) {
        kernel[i] /= sum;
    }

    return kernel;
}

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