org.apache.commons.math.distribution
Class AbstractIntegerDistribution

java.lang.Object
  extended by org.apache.commons.math.distribution.AbstractDistribution
      extended by org.apache.commons.math.distribution.AbstractIntegerDistribution
All Implemented Interfaces:
Serializable, DiscreteDistribution, Distribution, IntegerDistribution
Direct Known Subclasses:
BinomialDistributionImpl, HypergeometricDistributionImpl, PascalDistributionImpl, PoissonDistributionImpl, ZipfDistributionImpl

public abstract class AbstractIntegerDistribution
extends AbstractDistribution
implements IntegerDistribution, Serializable

Base class for integer-valued discrete distributions. Default implementations are provided for some of the methods that do not vary from distribution to distribution.

See Also:
Serialized Form

Method Summary
 double cumulativeProbability(double x)
          For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x).
 double cumulativeProbability(double x0, double x1)
          For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).
abstract  double cumulativeProbability(int x)
          For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x).
 double cumulativeProbability(int x0, int x1)
          For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).
 int inverseCumulativeProbability(double p)
          For a random variable X whose values are distributed according to this distribution, this method returns the largest x, such that P(X ≤ x) ≤ p.
 boolean isSupportLowerBoundInclusive()
          Use this method to get information about whether the lower bound of the support is inclusive or not.
 boolean isSupportUpperBoundInclusive()
          Use this method to get information about whether the upper bound of the support is inclusive or not.
 double probability(double x)
          For a random variable X whose values are distributed according to this distribution, this method returns P(X = x).
 void reseedRandomGenerator(long seed)
          Reseeds the random generator used to generate samples.
 int sample()
          Generates a random value sampled from this distribution.
 int[] sample(int sampleSize)
          Generates a random sample from the distribution.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface org.apache.commons.math.distribution.IntegerDistribution
probability
 

Method Detail

cumulativeProbability

public double cumulativeProbability(double x)
                             throws MathException
For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x). In other words, this method represents the (cumulative) distribution function, or CDF, for this distribution.

If x does not represent an integer value, the CDF is evaluated at the greatest integer less than x.

Specified by:
cumulativeProbability in interface Distribution
Parameters:
x - the value at which the distribution function is evaluated.
Returns:
cumulative probability that a random variable with this distribution takes a value less than or equal to x
Throws:
MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

cumulativeProbability

public double cumulativeProbability(double x0,
                                    double x1)
                             throws MathException
For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).

Specified by:
cumulativeProbability in interface Distribution
Overrides:
cumulativeProbability in class AbstractDistribution
Parameters:
x0 - the (inclusive) lower bound
x1 - the (inclusive) upper bound
Returns:
the probability that a random variable with this distribution will take a value between x0 and x1, including the endpoints.
Throws:
MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.
IllegalArgumentException - if x0 > x1

cumulativeProbability

public abstract double cumulativeProbability(int x)
                                      throws MathException
For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x). In other words, this method represents the probability distribution function, or PDF, for this distribution.

Specified by:
cumulativeProbability in interface IntegerDistribution
Parameters:
x - the value at which the PDF is evaluated.
Returns:
PDF for this distribution.
Throws:
MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

probability

public double probability(double x)
For a random variable X whose values are distributed according to this distribution, this method returns P(X = x). In other words, this method represents the probability mass function, or PMF, for the distribution.

If x does not represent an integer value, 0 is returned.

Specified by:
probability in interface DiscreteDistribution
Parameters:
x - the value at which the probability density function is evaluated
Returns:
the value of the probability density function at x

cumulativeProbability

public double cumulativeProbability(int x0,
                                    int x1)
                             throws MathException
For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).

Specified by:
cumulativeProbability in interface IntegerDistribution
Parameters:
x0 - the inclusive, lower bound
x1 - the inclusive, upper bound
Returns:
the cumulative probability.
Throws:
MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.
IllegalArgumentException - if x0 > x1

inverseCumulativeProbability

public int inverseCumulativeProbability(double p)
                                 throws MathException
For a random variable X whose values are distributed according to this distribution, this method returns the largest x, such that P(X ≤ x) ≤ p.

Specified by:
inverseCumulativeProbability in interface IntegerDistribution
Parameters:
p - the desired probability
Returns:
the largest x such that P(X ≤ x) <= p
Throws:
MathException - if the inverse cumulative probability can not be computed due to convergence or other numerical errors.
IllegalArgumentException - if p < 0 or p > 1

reseedRandomGenerator

public void reseedRandomGenerator(long seed)
Reseeds the random generator used to generate samples.

Parameters:
seed - the new seed
Since:
2.2

sample

public int sample()
           throws MathException
Generates a random value sampled from this distribution. The default implementation uses the inversion method.

Returns:
random value
Throws:
MathException - if an error occurs generating the random value
Since:
2.2

sample

public int[] sample(int sampleSize)
             throws MathException
Generates a random sample from the distribution. The default implementation generates the sample by calling sample() in a loop.

Parameters:
sampleSize - number of random values to generate
Returns:
an array representing the random sample
Throws:
MathException - if an error occurs generating the sample
IllegalArgumentException - if sampleSize is not positive
Since:
2.2

isSupportLowerBoundInclusive

public boolean isSupportLowerBoundInclusive()
Use this method to get information about whether the lower bound of the support is inclusive or not. For discrete support, only true here is meaningful.

Returns:
true (always but at Integer.MIN_VALUE because of the nature of discrete support)
Since:
2.2

isSupportUpperBoundInclusive

public boolean isSupportUpperBoundInclusive()
Use this method to get information about whether the upper bound of the support is inclusive or not. For discrete support, only true here is meaningful.

Returns:
true (always but at Integer.MAX_VALUE because of the nature of discrete support)
Since:
2.2


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