Numeric.SpecFunctions.Extra

math-functions-0.3.4.4: Collection of tools for numeric computations

Copyright | (c) 2009 2011 Bryan O'Sullivan
License | BSD3
Maintainer | bos@serpentine.com
Stability | experimental
Portability | portable
Safe Haskell | None
Language | Haskell2010

Numeric.SpecFunctions.Extra

Description

Less common mathematical functions.

Synopsis

- bd0 :: Double -> Double -> Double
- chooseExact :: Int -> Int -> Double
- logChooseFast :: Double -> Double -> Double
- logGammaAS245 :: Double -> Double
- logGammaCorrection :: Double -> Double

# Documentation

bd0 #

Arguments

:: Double |
    x
-> Double |
    np
-> Double |

Evaluate the deviance term `x log(x/np) + np - x`.

chooseExact :: Int -> Int -> Double #

Calculate binomial coefficient using exact formula

logChooseFast :: Double -> Double -> Double #

Quickly compute the natural logarithm of n ``choose`` k, with no checking.

Less numerically stable:

    exp $ lg (n+1) - lg (k+1) - lg (n-k+1)
      where lg = logGamma . fromIntegral

logGammaAS245 :: Double -> Double #

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).

logGammaCorrection :: Double -> Double #

Compute the log gamma correction factor for Stirling approximation for `x` ≥ 10. This correction factor is suitable for an alternate (but less numerically accurate) definition of `logGamma`:

\[ \log\Gamma(x) = \frac{1}{2}\log(2\pi) + (x-\frac{1}{2})\log x - x + \operatorname{logGammaCorrection}(x) \]