java.lang.Object
- org.apache.commons.statistics.distribution.AbstractContinuousDistribution
- - org.apache.commons.statistics.distribution.TriangularDistribution

All Implemented Interfaces:

ContinuousDistribution
```
public final class TriangularDistribution
extends AbstractContinuousDistribution
```
Implementation of the triangular distribution.
The probability density function of \( X \) is:
\[ f(x; a, b, c) = \begin{cases} \frac{2(x-a)}{(b-a)(c-a)} & \text{for } a \le x \lt c \\ \frac{2}{b-a} & \text{for } x = c \\ \frac{2(b-x)}{(b-a)(b-c)} & \text{for } c \lt x \le b \\ \end{cases} \]
for \( -\infty \lt a \le c \le b \lt \infty \) and \( x \in [a, b] \).

See Also:

Triangular distribution (Wikipedia), Triangular distribution (MathWorld)

Nested Class Summary
- Nested classes/interfaces inherited from interface org.apache.commons.statistics.distribution.ContinuousDistribution
  ContinuousDistribution.Sampler

Field Summary

Fields
Modifier and Type	Field	Description
`private double`	`a`	Lower limit of this distribution (inclusive).
`private double`	`b`	Upper limit of this distribution (inclusive).
`private double`	`c`	Mode of this distribution.
`private double`	`cdfMode`	Cumulative probability at the mode.
`private double`	`divisor1`	Cached value ((b - a) * (c - a).
`private double`	`divisor2`	Cached value ((b - a) * (b - c)).
`private double`	`sfMode`	Survival probability at the mode.

Constructor Summary

Constructors
Modifier Constructor Description

private TriangularDistribution(double a, double c, double b)

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`double`	`cumulativeProbability(double x)`	For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X <= x)`.
`double`	`density(double x)`	Returns the probability density function (PDF) of this distribution evaluated at the specified point `x`.
`double`	`getMean()`	Gets the mean of this distribution.
`double`	`getMode()`	Gets the mode parameter of this distribution.
`double`	`getSupportLowerBound()`	Gets the lower bound of the support.
`double`	`getSupportUpperBound()`	Gets the upper bound of the support.
`double`	`getVariance()`	Gets the variance of this distribution.
`double`	`inverseCumulativeProbability(double p)`	Computes the quantile function of this distribution.
`double`	`inverseSurvivalProbability(double p)`	Computes the inverse survival probability function of this distribution.
`static TriangularDistribution`	`of(double a, double c, double b)`	Creates a triangular distribution.
`double`	`survivalProbability(double x)`	For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X > x)`.

Methods inherited from class org.apache.commons.statistics.distribution.AbstractContinuousDistribution
createSampler, getMedian, isSupportConnected, probability

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.commons.statistics.distribution.ContinuousDistribution
logDensity

- Field Detail
  - a
```
private final double a
```
    Lower limit of this distribution (inclusive).
  - b
```
private final double b
```
    Upper limit of this distribution (inclusive).
  - c
```
private final double c
```
    Mode of this distribution.
  - divisor1
```
private final double divisor1
```
    Cached value ((b - a) * (c - a).
  - divisor2
```
private final double divisor2
```
    Cached value ((b - a) * (b - c)).
  - cdfMode
```
private final double cdfMode
```
    Cumulative probability at the mode.
  - sfMode
```
private final double sfMode
```
    Survival probability at the mode.
- Constructor Detail
  - TriangularDistribution
```
private TriangularDistribution(double a,
                               double c,
                               double b)
```
    Parameters:
    
    a - Lower limit of this distribution (inclusive).
    
    c - Mode of this distribution.
    
    b - Upper limit of this distribution (inclusive).
- Method Detail
  - of
```
public static TriangularDistribution of(double a,
                                        double c,
                                        double b)
```
    Creates a triangular distribution.
    
    Parameters:
    
    a - Lower limit of this distribution (inclusive).
    
    c - Mode of this distribution.
    
    b - Upper limit of this distribution (inclusive).
    
    Returns:
    
    the distribution
    
    Throws:
    
    java.lang.IllegalArgumentException - if a >= b, if c > b or if c < a.
  - getMode
```
public double getMode()
```
    Gets the mode parameter of this distribution.
    
    Returns:
    
    the mode.
  - density
```
public double density(double x)
```
    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 - Point at which the PDF is evaluated.
    
    Returns:
    
    the value of the probability density function at x.
  - cumulativeProbability
```
public double cumulativeProbability(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 (cumulative) distribution function (CDF) for this distribution.
    
    Parameters:
    
    x - Point at which the CDF is evaluated.
    
    Returns:
    
    the probability that a random variable with this distribution takes a value less than or equal to x.
  - survivalProbability
```
public double survivalProbability(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 complementary cumulative distribution function.
    By default, this is defined as 1 - cumulativeProbability(x), but the specific implementation may be more accurate.
    
    Parameters:
    
    x - Point at which the survival function is evaluated.
    
    Returns:
    
    the probability that a random variable with this distribution takes a value greater than x.
  - inverseCumulativeProbability
```
public double inverseCumulativeProbability(double p)
```
    Computes the quantile function of this distribution. For a random variable X distributed according to this distribution, the returned value is:
    \[ x = \begin{cases} \inf \{ x \in \mathbb R : P(X \le x) \ge p\} & \text{for } 0 \lt p \le 1 \\ \inf \{ x \in \mathbb R : P(X \le x) \gt 0 \} & \text{for } p = 0 \end{cases} \]
    The default implementation returns:
    
    ContinuousDistribution.getSupportLowerBound() for p = 0,
    
    ContinuousDistribution.getSupportUpperBound() for p = 1, or
    
    the result of a search for a root between the lower and upper bound using cumulativeProbability(x) - p. The bounds may be bracketed for efficiency.
    Specified by:
    
    inverseCumulativeProbability in interface ContinuousDistribution
    
    Overrides:
    
    inverseCumulativeProbability in class AbstractContinuousDistribution
    
    Parameters:
    
    p - Cumulative probability.
    
    Returns:
    
    the smallest p-quantile of this distribution (largest 0-quantile for p = 0).
  - inverseSurvivalProbability
```
public double inverseSurvivalProbability(double p)
```
    Computes the inverse survival probability function of this distribution. For a random variable X distributed according to this distribution, the returned value is:
    \[ x = \begin{cases} \inf \{ x \in \mathbb R : P(X \gt x) \le p\} & \text{for } 0 \le p \lt 1 \\ \inf \{ x \in \mathbb R : P(X \gt x) \lt 1 \} & \text{for } p = 1 \end{cases} \]
    By default, this is defined as inverseCumulativeProbability(1 - p), but the specific implementation may be more accurate.
    The default implementation returns:
    
    ContinuousDistribution.getSupportLowerBound() for p = 1,
    
    ContinuousDistribution.getSupportUpperBound() for p = 0, or
    
    the result of a search for a root between the lower and upper bound using survivalProbability(x) - p. The bounds may be bracketed for efficiency.
    Specified by:
    
    inverseSurvivalProbability in interface ContinuousDistribution
    
    Overrides:
    
    inverseSurvivalProbability in class AbstractContinuousDistribution
    
    Parameters:
    
    p - Survival probability.
    
    Returns:
    
    the smallest (1-p)-quantile of this distribution (largest 0-quantile for p = 1).
  - getMean
```
public double getMean()
```
    Gets the mean of this distribution.
    For lower limit \( a \), upper limit \( b \), and mode \( c \), the mean is \( (a + b + c) / 3 \).
    
    Returns:
    
    the mean.
  - getVariance
```
public double getVariance()
```
    Gets the variance of this distribution.
    For lower limit \( a \), upper limit \( b \), and mode \( c \), the variance is \( (a^2 + b^2 + c^2 - ab - ac - bc) / 18 \).
    
    Returns:
    
    the variance.
  - getSupportLowerBound
```
public double getSupportLowerBound()
```
    Gets the lower bound of the support. It must return the same value as inverseCumulativeProbability(0), i.e. \( \inf \{ x \in \mathbb R : P(X \le x) \gt 0 \} \).
    The lower bound of the support is equal to the lower limit parameter a of the distribution.
    
    Returns:
    
    the lower bound of the support.
  - getSupportUpperBound
```
public double getSupportUpperBound()
```
    Gets the upper bound of the support. It must return the same value as inverseCumulativeProbability(1), i.e. \( \inf \{ x \in \mathbb R : P(X \le x) = 1 \} \).
    The upper bound of the support is equal to the upper limit parameter b of the distribution.
    
    Returns:
    
    the upper bound of the support.

Class TriangularDistribution

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.commons.statistics.distribution.ContinuousDistribution

Field Summary

Constructor Summary

Method Summary

Methods inherited from class org.apache.commons.statistics.distribution.AbstractContinuousDistribution

Methods inherited from class java.lang.Object

Methods inherited from interface org.apache.commons.statistics.distribution.ContinuousDistribution

Field Detail

a

b

c

divisor1

divisor2

cdfMode

sfMode

Constructor Detail

TriangularDistribution

Method Detail

of

getMode

density

cumulativeProbability

survivalProbability

inverseCumulativeProbability

inverseSurvivalProbability

getMean

getVariance

getSupportLowerBound

getSupportUpperBound