public double logDensity()

in commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/GammaDistribution.java [139:161]

• 17 lines of code
• 7 McCabe index (conditional complexity)

    public double logDensity(double x) {
        if (x <= SUPPORT_LO ||
            x >= SUPPORT_HI) {
            // Special case x=0
            if (x == SUPPORT_LO && shape <= 1) {
                return shape == 1 ?
                    -Math.log(scale) :
                    Double.POSITIVE_INFINITY;
            }
            return Double.NEGATIVE_INFINITY;
        }

        final double y = x / scale;

        // More accurate to log the density when it is finite.
        // See NUMBERS-174: 'Log of the Gamma P Derivative'
        final double p = RegularizedGamma.P.derivative(shape, y) / scale;
        if (p <= Double.MAX_VALUE && p >= Double.MIN_NORMAL) {
            return Math.log(p);
        }
        // Use the log computation
        return minusLogGammaShapeMinusLogScale - y + Math.log(y) * (shape - 1);
    }