How to use

logBeta

method

in

org.apache.commons.math3.special.Beta

/**
 * Returns the natural logarithm of the beta function B(a, b).
 *
 * The implementation of this method is based on:
 * <ul>
 * <li><a href="http://mathworld.wolfram.com/BetaFunction.html">
 * Beta Function</a>, equation (1).</li>
 * </ul>
 *
 * @param a Parameter {@code a}.
 * @param b Parameter {@code b}.
 * @param epsilon This parameter is ignored.
 * @param maxIterations This parameter is ignored.
 * @return log(B(a, b)).
 * @deprecated as of version 3.1, this method is deprecated as the
 * computation of the beta function is no longer iterative; it will be
 * removed in version 4.0. Current implementation of this method
 * internally calls {@link #logBeta(double, double)}.
 */
@Deprecated
public static double logBeta(double a, double b,
               double epsilon,
               int maxIterations) {
  return logBeta(a, b);
}

/** {@inheritDoc} **/
@Override
public double logDensity(double x) {
  final double nhalf = numeratorDegreesOfFreedom / 2;
  final double mhalf = denominatorDegreesOfFreedom / 2;
  final double logx = FastMath.log(x);
  final double logn = FastMath.log(numeratorDegreesOfFreedom);
  final double logm = FastMath.log(denominatorDegreesOfFreedom);
  final double lognxm = FastMath.log(numeratorDegreesOfFreedom * x +
      denominatorDegreesOfFreedom);
  return nhalf * logn + nhalf * logx - logx +
      mhalf * logm - nhalf * lognxm - mhalf * lognxm -
      Beta.logBeta(nhalf, mhalf);
}

FastMath.log(a) - logBeta(a, b)) *
1.0 / fraction.evaluate(x, epsilon, maxIterations);

final public static double beta(double a, double b) {
  return Math.exp(Beta.logBeta(a, b));
}

/**
 * Returns the natural logarithm of the beta function B(a, b).
 *
 * The implementation of this method is based on:
 * <ul>
 * <li><a href="http://mathworld.wolfram.com/BetaFunction.html">
 * Beta Function</a>, equation (1).</li>
 * </ul>
 *
 * @param a Parameter {@code a}.
 * @param b Parameter {@code b}.
 * @param epsilon This parameter is ignored.
 * @param maxIterations This parameter is ignored.
 * @return log(B(a, b)).
 * @deprecated as of version 3.1, this method is deprecated as the
 * computation of the beta function is no longer iterative; it will be
 * removed in version 4.0. Current implementation of this method
 * internally calls {@link #logBeta(double, double)}.
 */
@Deprecated
public static double logBeta(double a, double b,
               double epsilon,
               int maxIterations) {
  return logBeta(a, b);
}

/** {@inheritDoc} **/
@Override
public double logDensity(double x) {
  final double nhalf = numeratorDegreesOfFreedom / 2;
  final double mhalf = denominatorDegreesOfFreedom / 2;
  final double logx = Math.log(x);
  final double logn = Math.log(numeratorDegreesOfFreedom);
  final double logm = Math.log(denominatorDegreesOfFreedom);
  final double lognxm = Math.log(numeratorDegreesOfFreedom * x +
      denominatorDegreesOfFreedom);
  return nhalf * logn + nhalf * logx - logx +
      mhalf * logm - nhalf * lognxm - mhalf * lognxm -
      Beta.logBeta(nhalf, mhalf);
}

/**
 * Returns the natural logarithm of the beta function B(a, b).
 *
 * The implementation of this method is based on:
 * <ul>
 * <li><a href="http://mathworld.wolfram.com/BetaFunction.html">
 * Beta Function</a>, equation (1).</li>
 * </ul>
 *
 * @param a Parameter {@code a}.
 * @param b Parameter {@code b}.
 * @param epsilon This parameter is ignored.
 * @param maxIterations This parameter is ignored.
 * @return log(B(a, b)).
 * @deprecated as of version 3.1, this method is deprecated as the
 * computation of the beta function is no longer iterative; it will be
 * removed in version 4.0. Current implementation of this method
 * internally calls {@link #logBeta(double, double)}.
 */
@Deprecated
public static double logBeta(double a, double b,
               double epsilon,
               int maxIterations) {
  return logBeta(a, b);
}

Math.log(a) - logBeta(a, b)) *
1.0 / fraction.evaluate(x, epsilon, maxIterations);

/** {@inheritDoc} **/
@Override
public double logDensity(double x) {
  final double nhalf = numeratorDegreesOfFreedom / 2;
  final double mhalf = denominatorDegreesOfFreedom / 2;
  final double logx = FastMath.log(x);
  final double logn = FastMath.log(numeratorDegreesOfFreedom);
  final double logm = FastMath.log(denominatorDegreesOfFreedom);
  final double lognxm = FastMath.log(numeratorDegreesOfFreedom * x +
      denominatorDegreesOfFreedom);
  return nhalf * logn + nhalf * logx - logx +
      mhalf * logm - nhalf * lognxm - mhalf * lognxm -
      Beta.logBeta(nhalf, mhalf);
}

FastMath.log(a) - logBeta(a, b)) *
1.0 / fraction.evaluate(x, epsilon, maxIterations);