Copyright | (c) 2016 Alexey Khudyakov |
---|---|

License | BSD3 |

Maintainer | alexey.skladnoy@gmail.com, bos@serpentine.com |

Stability | experimental |

Portability | portable |

Safe Haskell | Safe |

Language | Haskell2010 |

Functions for working with infinite sequences. In particular summation of series and evaluation of continued fractions.

- data Sequence a = Sequence s (s -> (a, s))
- enumSequenceFrom :: Num a => a -> Sequence a
- enumSequenceFromStep :: Num a => a -> a -> Sequence a
- scanSequence :: (b -> a -> b) -> b -> Sequence a -> Sequence b
- sumSeries :: Sequence Double -> Double
- sumPowerSeries :: Double -> Sequence Double -> Double
- sequenceToList :: Sequence a -> [a]
- evalContFractionB :: Sequence (Double, Double) -> Double

# Data type for infinite sequences.

Infinite series. It's represented as opaque state and step function.

Sequence s (s -> (a, s)) |

Functor Sequence # | |

Applicative Sequence # | |

Fractional a => Fractional (Sequence a) # | Elementwise operations with sequences |

Num a => Num (Sequence a) # | Elementwise operations with sequences |

# Constructors

enumSequenceFrom :: Num a => a -> Sequence a #

`enumSequenceFrom x`

generate sequence:

\[ a_n = x + n \]

enumSequenceFromStep :: Num a => a -> a -> Sequence a #

`enumSequenceFromStep x d`

generate sequence:

\[ a_n = x + nd \]

scanSequence :: (b -> a -> b) -> b -> Sequence a -> Sequence b #

Analog of `scanl`

for sequence.

# Summation of series

sumSeries :: Sequence Double -> Double #

Calculate sum of series

\[ \sum_{i=0}^\infty a_i \]

Summation is stopped when

\[ a_{n+1} < \varepsilon\sum_{i=0}^n a_i \]

where ε is machine precision (`m_epsilon`

)

sumPowerSeries :: Double -> Sequence Double -> Double #

Calculate sum of series

\[ \sum_{i=0}^\infty x^ia_i \]

Calculation is stopped when next value in series is less than ε·sum.

sequenceToList :: Sequence a -> [a] #

Convert series to infinite list

# Evaluation of continued fractions

evalContFractionB :: Sequence (Double, Double) -> Double #

Evaluate continued fraction using modified Lentz algorithm. Sequence contain pairs (a[i],b[i]) which form following expression:

\[ b_0 + \frac{a_1}{b_1+\frac{a_2}{b_2+\frac{a_3}{b_3 + \cdots}}} \]

Modified Lentz algorithm is described in Numerical recipes 5.2 "Evaluation of Continued Fractions"