Top Description Fields Constructors Methods
org.apache.commons.math3.distribution

public Class NormalDistribution

extends AbstractRealDistribution
Class Inheritance
Imports
org.apache.commons.math3.exception.NotStrictlyPositiveException, .NumberIsTooLargeException, .OutOfRangeException, org.apache.commons.math3.exception.util.LocalizedFormats, org.apache.commons.math3.random.RandomGenerator, .Well19937c, org.apache.commons.math3.special.Erf, org.apache.commons.math3.util.FastMath

Implementation of the normal (gaussian) distribution.
See Also
Normal distribution (Wikipedia), Normal distribution (MathWorld)

Field Summary

Modifier and TypeField and Description
public static final double
DEFAULT_INVERSE_ABSOLUTE_ACCURACY

Default inverse cumulative probability accuracy.

private final double
logStandardDeviationPlusHalfLog2Pi

The value of log(sd) + 0.5*log(2*pi) stored for faster computation.

private final double
mean

Mean of this distribution.

private static final long
private final double
private static final double
SQRT2

√(2)

private final double
standardDeviation

Standard deviation of this distribution.

Inherited from org.apache.commons.math3.distribution.AbstractRealDistribution:
randomrandomDataSOLVER_DEFAULT_ABSOLUTE_ACCURACY

Constructor Summary

AccessConstructor and Description
public
NormalDistribution()

Create a normal distribution with mean equal to zero and standard deviation equal to one.

public
NormalDistribution(double
Mean for this distribution.
mean
,
double
Standard deviation for this distribution.
sd
)

Create a normal distribution using the given mean and standard deviation.

public
NormalDistribution(double
Mean for this distribution.
mean
,
double
Standard deviation for this distribution.
sd
,
double
Inverse cumulative probability accuracy.
inverseCumAccuracy
)

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

public
NormalDistribution(RandomGenerator
Random number generator.
rng
,
double
Mean for this distribution.
mean
,
double
Standard deviation for this distribution.
sd
)

Creates a normal distribution.

public
NormalDistribution(RandomGenerator
Random number generator.
rng
,
double
Mean for this distribution.
mean
,
double
Standard deviation for this distribution.
sd
,
double
Inverse cumulative probability accuracy.
inverseCumAccuracy
)

Creates a normal distribution.

Method Summary

Modifier and TypeMethod and Description
public double
cumulativeProbability(double
the point at which the CDF is evaluated
x
)

Implements org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

For a random variable X whose values are distributed according to this distribution, this method returns P(X <= x).

public double
cumulativeProbability(double
the exclusive lower bound
x0
,
double
the inclusive upper bound
x1
)

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.cumulativeProbability.

Implements org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 < X <= x1).

public double
density(double
the point at which the PDF is evaluated
x
)

Implements org.apache.commons.math3.distribution.RealDistribution.density.

Returns the probability density function (PDF) of this distribution evaluated at the specified point x.

public double

Returns:

the mean for this distribution.
getMean
()

Access the mean.

public double
getNumericalMean()

Implements org.apache.commons.math3.distribution.RealDistribution.getNumericalMean.

Use this method to get the numerical value of the mean of this distribution.

public double
getNumericalVariance()

Implements org.apache.commons.math3.distribution.RealDistribution.getNumericalVariance.

Use this method to get the numerical value of the variance of this distribution.

protected double
getSolverAbsoluteAccuracy()

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.getSolverAbsoluteAccuracy.

Returns the solver absolute accuracy for inverse cumulative computation.

public double

Returns:

the standard deviation for this distribution.
getStandardDeviation
()

Access the standard deviation.

public double

Returns:

lower bound of the support (always Double.NEGATIVE_INFINITY)
getSupportLowerBound
()

Implements org.apache.commons.math3.distribution.RealDistribution.getSupportLowerBound.

Access the lower bound of the support.

public double

Returns:

upper bound of the support (always Double.POSITIVE_INFINITY)
getSupportUpperBound
()

Implements org.apache.commons.math3.distribution.RealDistribution.getSupportUpperBound.

Access the upper bound of the support.

public double
public boolean

Returns:

true
isSupportConnected
()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportConnected.

Use this method to get information about whether the support is connected, i.e. whether all values between the lower and upper bound of the support are included in the support.

public boolean
isSupportLowerBoundInclusive()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportLowerBoundInclusive.

Whether or not the lower bound of support is in the domain of the density function.

public boolean
isSupportUpperBoundInclusive()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportUpperBoundInclusive.

Whether or not the upper bound of support is in the domain of the density function.

public double
logDensity(double
the point at which the PDF is evaluated
x
)

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.logDensity.

Returns the natural logarithm of the probability density function (PDF) of this distribution evaluated at the specified point x.

public double
probability(double
Lower bound (excluded).
x0
,
double
Upper bound (included).
x1
)

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.probability.

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 < X <= x1).

public double
Inherited from org.apache.commons.math3.distribution.AbstractRealDistribution:
probabilityreseedRandomGeneratorsample

Field Detail

DEFAULT_INVERSE_ABSOLUTE_ACCURACYback to summary
public static final double DEFAULT_INVERSE_ABSOLUTE_ACCURACY

Default inverse cumulative probability accuracy.

Since
2.1
logStandardDeviationPlusHalfLog2Piback to summary
private final double logStandardDeviationPlusHalfLog2Pi

The value of log(sd) + 0.5*log(2*pi) stored for faster computation.

meanback to summary
private final double mean

Mean of this distribution.

serialVersionUIDback to summary
private static final long serialVersionUID

Hides org.apache.commons.math3.distribution.AbstractRealDistribution.serialVersionUID.

Serializable version identifier.

solverAbsoluteAccuracyback to summary
private final double solverAbsoluteAccuracy

Hides org.apache.commons.math3.distribution.AbstractRealDistribution.solverAbsoluteAccuracy.

Inverse cumulative probability accuracy.

SQRT2back to summary
private static final double SQRT2

√(2)

standardDeviationback to summary
private final double standardDeviation

Standard deviation of this distribution.

Constructor Detail

NormalDistributionback to summary
public NormalDistribution()

Create a normal distribution with mean equal to zero and standard deviation equal to one.

Note

this constructor will implicitly create an instance of Well19937c as random generator to be used for sampling only (see sample() and sample(int)). In case no sampling is needed for the created distribution, it is advised to pass null as random generator via the appropriate constructors to avoid the additional initialisation overhead.

NormalDistributionback to summary
public NormalDistribution(double mean, double sd) throws NotStrictlyPositiveException

Create a normal distribution using the given mean and standard deviation.

Note

this constructor will implicitly create an instance of Well19937c as random generator to be used for sampling only (see sample() and sample(int)). In case no sampling is needed for the created distribution, it is advised to pass null as random generator via the appropriate constructors to avoid the additional initialisation overhead.

Parameters
mean:double

Mean for this distribution.

sd:double

Standard deviation for this distribution.

Exceptions
NotStrictlyPositiveException:
if sd <= 0.
NormalDistributionback to summary
public NormalDistribution(double mean, double sd, double inverseCumAccuracy) throws NotStrictlyPositiveException

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

Note

this constructor will implicitly create an instance of Well19937c as random generator to be used for sampling only (see sample() and sample(int)). In case no sampling is needed for the created distribution, it is advised to pass null as random generator via the appropriate constructors to avoid the additional initialisation overhead.

Parameters
mean:double

Mean for this distribution.

sd:double

Standard deviation for this distribution.

inverseCumAccuracy:double

Inverse cumulative probability accuracy.

Exceptions
NotStrictlyPositiveException:
if sd <= 0.
Since
2.1
NormalDistributionback to summary
public NormalDistribution(RandomGenerator rng, double mean, double sd) throws NotStrictlyPositiveException

Creates a normal distribution.

Parameters
rng:RandomGenerator

Random number generator.

mean:double

Mean for this distribution.

sd:double

Standard deviation for this distribution.

Exceptions
NotStrictlyPositiveException:
if sd <= 0.
Since
3.3
NormalDistributionback to summary
public NormalDistribution(RandomGenerator rng, double mean, double sd, double inverseCumAccuracy) throws NotStrictlyPositiveException

Creates a normal distribution.

Parameters
rng:RandomGenerator

Random number generator.

mean:double

Mean for this distribution.

sd:double

Standard deviation for this distribution.

inverseCumAccuracy:double

Inverse cumulative probability accuracy.

Exceptions
NotStrictlyPositiveException:
if sd <= 0.
Since
3.1

Method Detail

cumulativeProbabilityback to summary
public double cumulativeProbability(double x)

Implements org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

Doc from org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

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 (CDF) for this distribution. If x is more than 40 standard deviations from the mean, 0 or 1 is returned, as in these cases the actual value is within Double.MIN_VALUE of 0 or 1.

Parameters
x:double

the point at which the CDF is evaluated

Returns:double

the probability that a random variable with this distribution takes a value less than or equal to x

cumulativeProbabilityback to summary
public double cumulativeProbability(double x0, double x1) throws NumberIsTooLargeException

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.cumulativeProbability.

Implements org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.cumulativeProbability.

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 < X <= x1). The default implementation uses the identity

P(x0 < X <= x1) = P(X <= x1) - P(X <= x0)

Parameters
x0:double

Doc from org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

the exclusive lower bound

x1:double

Doc from org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

the inclusive upper bound

Returns:double

Doc from org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

the probability that a random variable with this distribution takes a value between x0 and x1, excluding the lower and including the upper endpoint

Annotations
@Override
@Deprecated
Exceptions
NumberIsTooLargeException:

Doc from org.apache.commons.math3.distribution.RealDistribution.cumulativeProbability.

if x0 > x1

densityback to summary
public double density(double x)

Implements org.apache.commons.math3.distribution.RealDistribution.density.

Doc from org.apache.commons.math3.distribution.RealDistribution.density.

Returns the probability density function (PDF) of this distribution evaluated at the specified point x. In general, the PDF is the derivative of the CDF. If the derivative does not exist at x, then an appropriate replacement should be returned, e.g. Double.POSITIVE_INFINITY, Double.NaN, or the limit inferior or limit superior of the difference quotient.

Parameters
x:double

the point at which the PDF is evaluated

Returns:double

the value of the probability density function at point x

getMeanback to summary
public double getMean()

Access the mean.

Returns:double

the mean for this distribution.

getNumericalMeanback to summary
public double getNumericalMean()

Implements org.apache.commons.math3.distribution.RealDistribution.getNumericalMean.

Doc from org.apache.commons.math3.distribution.RealDistribution.getNumericalMean.

Use this method to get the numerical value of the mean of this distribution. For mean parameter mu, the mean is mu.

Returns:double

the mean or Double.NaN if it is not defined

getNumericalVarianceback to summary
public double getNumericalVariance()

Implements org.apache.commons.math3.distribution.RealDistribution.getNumericalVariance.

Doc from org.apache.commons.math3.distribution.RealDistribution.getNumericalVariance.

Use this method to get the numerical value of the variance of this distribution. For standard deviation parameter s, the variance is s^2.

Returns:double

the variance (possibly Double.POSITIVE_INFINITY as for certain cases in TDistribution) or Double.NaN if it is not defined

getSolverAbsoluteAccuracyback to summary
protected double getSolverAbsoluteAccuracy()

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.getSolverAbsoluteAccuracy.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.getSolverAbsoluteAccuracy.

Returns the solver absolute accuracy for inverse cumulative computation. You can override this method in order to use a Brent solver with an absolute accuracy different from the default.

Returns:double

the maximum absolute error in inverse cumulative probability estimates

Annotations
@Override
getStandardDeviationback to summary
public double getStandardDeviation()

Access the standard deviation.

Returns:double

the standard deviation for this distribution.

getSupportLowerBoundback to summary
public double getSupportLowerBound()

Implements org.apache.commons.math3.distribution.RealDistribution.getSupportLowerBound.

Doc from org.apache.commons.math3.distribution.RealDistribution.getSupportLowerBound.

Access the lower bound of the support. This method must return the same value as inverseCumulativeProbability(0). In other words, this method must return

inf {x in R | P(X <= x) > 0}.

The lower bound of the support is always negative infinity no matter the parameters.
Returns:double

lower bound of the support (always Double.NEGATIVE_INFINITY)

getSupportUpperBoundback to summary
public double getSupportUpperBound()

Implements org.apache.commons.math3.distribution.RealDistribution.getSupportUpperBound.

Doc from org.apache.commons.math3.distribution.RealDistribution.getSupportUpperBound.

Access the upper bound of the support. This method must return the same value as inverseCumulativeProbability(1). In other words, this method must return

inf {x in R | P(X <= x) = 1}.

The upper bound of the support is always positive infinity no matter the parameters.
Returns:double

upper bound of the support (always Double.POSITIVE_INFINITY)

inverseCumulativeProbabilityback to summary
public double inverseCumulativeProbability(final double p) throws OutOfRangeException

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.inverseCumulativeProbability.

Implements org.apache.commons.math3.distribution.RealDistribution.inverseCumulativeProbability.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.inverseCumulativeProbability.

Computes the quantile function of this distribution. For a random variable X distributed according to this distribution, the returned value is

  • inf{x in R | P(X<=x) >= p} for 0 < p <= 1,
  • inf{x in R | P(X<=x) > 0} for p = 0.
The default implementation returns
Parameters
p:double

Doc from org.apache.commons.math3.distribution.RealDistribution.inverseCumulativeProbability.

the cumulative probability

Returns:double

Doc from org.apache.commons.math3.distribution.RealDistribution.inverseCumulativeProbability.

the smallest p-quantile of this distribution (largest 0-quantile for p = 0)

Annotations
@Override
Exceptions
OutOfRangeException:

Doc from org.apache.commons.math3.distribution.RealDistribution.inverseCumulativeProbability.

if p < 0 or p > 1

Since
3.2
isSupportConnectedback to summary
public boolean isSupportConnected()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportConnected.

Doc from org.apache.commons.math3.distribution.RealDistribution.isSupportConnected.

Use this method to get information about whether the support is connected, i.e. whether all values between the lower and upper bound of the support are included in the support. The support of this distribution is connected.

Returns:boolean

true

isSupportLowerBoundInclusiveback to summary
public boolean isSupportLowerBoundInclusive()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportLowerBoundInclusive.

Doc from org.apache.commons.math3.distribution.RealDistribution.isSupportLowerBoundInclusive.

Whether or not the lower bound of support is in the domain of the density function. Returns true iff getSupporLowerBound() is finite and density(getSupportLowerBound()) returns a non-NaN, non-infinite value.

Returns:boolean

true if the lower bound of support is finite and the density function returns a non-NaN, non-infinite value there

isSupportUpperBoundInclusiveback to summary
public boolean isSupportUpperBoundInclusive()

Implements org.apache.commons.math3.distribution.RealDistribution.isSupportUpperBoundInclusive.

Doc from org.apache.commons.math3.distribution.RealDistribution.isSupportUpperBoundInclusive.

Whether or not the upper bound of support is in the domain of the density function. Returns true iff getSupportUpperBound() is finite and density(getSupportUpperBound()) returns a non-NaN, non-infinite value.

Returns:boolean

true if the upper bound of support is finite and the density function returns a non-NaN, non-infinite value there

logDensityback to summary
public double logDensity(double x)

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.logDensity.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.logDensity.

Returns the natural logarithm of the probability density function (PDF) of this distribution evaluated at the specified point x. In general, the PDF is the derivative of the CDF. If the derivative does not exist at x, then an appropriate replacement should be returned, e.g. Double.POSITIVE_INFINITY, Double.NaN, or the limit inferior or limit superior of the difference quotient. Note that due to the floating point precision and under/overflow issues, this method will for some distributions be more precise and faster than computing the logarithm of density(double). The default implementation simply computes the logarithm of density(x).

Parameters
x:double

the point at which the PDF is evaluated

Returns:double

the logarithm of the value of the probability density function at point x

Annotations
@Override
probabilityback to summary
public double probability(double x0, double x1) throws NumberIsTooLargeException

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.probability.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.probability.

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 < X <= x1).

Parameters
x0:double

Lower bound (excluded).

x1:double

Upper bound (included).

Returns:double

the probability that a random variable with this distribution takes a value between x0 and x1, excluding the lower and including the upper endpoint.

Annotations
@Override
Exceptions
NumberIsTooLargeException:
if x0 > x1. The default implementation uses the identity P(x0 < X <= x1) = P(X <= x1) - P(X <= x0)
sampleback to summary
public double sample()

Overrides org.apache.commons.math3.distribution.AbstractRealDistribution.sample.

Implements org.apache.commons.math3.distribution.RealDistribution.sample.

Doc from org.apache.commons.math3.distribution.AbstractRealDistribution.sample.

Generate a random value sampled from this distribution. The default implementation uses the inversion method.

Returns:double

Doc from org.apache.commons.math3.distribution.RealDistribution.sample.

a random value.

Annotations
@Override