Portability | portable |
---|---|

Stability | experimental |

Maintainer | bos@serpentine.com |

Mathematical functions for statistics.

# Functions

:: Double | Parameter of each function. |

-> UArr Double | Coefficients of each polynomial term, in increasing order. |

-> Double |

Evaluate a series of Chebyshev polynomials. Uses Clenshaw's algorithm.

## Factorial functions

factorial :: Int -> DoubleSource

Compute the factorial function *n*!. Returns ∞ if the
input is above 170 (above which the result cannot be represented by
a 64-bit `Double`

).

logFactorial :: Int -> DoubleSource

Compute the natural logarithm of the factorial function. Gives 16 decimal digits of precision.

## Gamma functions

Compute the incomplete gamma integral function γ(*s*,*x*).
Uses Algorithm AS 239 by Shea.

logGamma :: Double -> DoubleSource

Compute the logarithm of the gamma function Γ(*x*). Uses
Algorithm AS 245 by Macleod.

Gives an accuracy of 10–12 significant decimal digits, except
for small regions around *x* = 1 and *x* = 2, where the function
goes to zero. For greater accuracy, use `logGammaL`

.

Returns ∞ if the input is outside of the range (0 < *x*
≤ 1e305).

logGammaL :: Double -> DoubleSource

Compute the logarithm of the gamma function, Γ(*x*). Uses a
Lanczos approximation.

This function is slower than `logGamma`

, but gives 14 or more
significant decimal digits of accuracy, except around *x* = 1 and
*x* = 2, where the function goes to zero.

Returns ∞ if the input is outside of the range (0 < *x*
≤ 1e305).

# References

- Clenshaw, C.W. (1962) Chebyshev series for mathematical
functions.
*National Physical Laboratory Mathematical Tables 5*, Her Majesty's Stationery Office, London. - Lanczos, C. (1964) A precision approximation of the gamma
function.
*SIAM Journal on Numerical Analysis B*1:86–96. http://www.jstor.org/stable/2949767 - Macleod, A.J. (1989) Algorithm AS 245: A robust and reliable
algorithm for the logarithm of the gamma function.
*Journal of the Royal Statistical Society, Series C (Applied Statistics)*38(2):397–402. http://www.jstor.org/stable/2348078 - Shea, B. (1988) Algorithm AS 239: Chi-squared and incomplete
gamma integral.
*Applied Statistics*37(3):466–473. http://www.jstor.org/stable/2347328