# The tensor package

This library defines data types and classes for fixed dimension vectors and tensors. The main objects are:

[@'Data.Ordinal.Ordinal'@] A totally ordered set with fixed size. The @'Data.Ordinal.Ordinal'@ type @'Data.Ordinal.One'@ contains 1 element, @'Data.Ordinal.Succ' 'Data.Ordinal.One'@ contains 2 elements, @'Data.Ordinal.Succ' 'Data.Ordinal.Succ' 'Data.Ordinal.One'@ contains 3 elements, and so on (see "Data.Ordinal" for more details). The type @'Data.Ordinal.Two'@ is an alias for @'Data.Ordinal.Succ' 'Data.Ordinal.One'@, @'Data.Ordinal.Three'@ is an alias for @'Data.Ordinal.Succ' 'Data.Ordinal.Succ' 'Data.Ordinal.One'@, and so on.

[@'Data.TypeList.MultiIndex.MultiIndex'@] The index set. It can be linear, rectangular, parallelepipedal, etc. The dimensions of the sides are expressed using @'Data.Ordinal.Ordinal'@ types and the type constructor @'Data.TypeList.MultiIndex.:|:'@, e.g. @('Data.Ordinal.Two' 'Data.TypeList.MultiIndex.:|:' ('Data.Ordinal.Three' 'Data.TypeList.MultiIndex.:|:' 'Data.TypeList.MultiIndex.Nil'))@ is a rectangular index set with 2 rows and 3 columns. The index set also contains elements, for example @('Data.Ordinal.Two' 'Data.TypeList.MultiIndex.:|:' ('Data.Ordinal.Three' 'Data.TypeList.MultiIndex.:|:' 'Data.TypeList.MultiIndex.Nil'))@ contains all the pairs @(i 'Data.TypeList.MultiIndex.:|:' (j 'Data.TypeList.MultiIndex.:|:' Nil))@ where i is in @'Data.Ordinal.Two'@ and j is in @'Data.Ordinal.Three'@. See "Data.TypeList.MultiIndex" for more details.

[@'Data.Tensor.Tensor'@] It is an assignment of elements to each element of its @'Data.TypeList.MultiIndex.MultiIndex'@.

Objects like vectors and matrices are special cases of tensors. Most of the functions to manipulate tensors are grouped into type classes. This allow the possibility of having different internal representations (backends) of a tensor, and act on these with the same functions. At the moment we only provide one backend based on <http://hackage.haskell.org/package/vector>, which is accessible by importing the module "Data.Tensor.Vector". More backends will be provided in future releases.

Here is a usage example:

>>> :m Data.Ordinal Data.TypeList.MultiIndex Data.Tensor.Vector >>> fromList [2,3,5,1,3,6,0,5,4,2,1,3] :: Tensor (Four :|: (Three :|: Nil)) Int [[2,3,5],[1,3,6],[0,5,4],[2,1,3]]

The above defines a tensor with 4 rows and 3 columns (a matrix) and @'Int'@ coefficients. The entries of this matrix are taken from a list using @'Data.Tensor.fromList'@ which is a method of the class @'Data.Tensor.FromList'@. Notice the output: the @'Show'@ instance is defined in such a way to give a readable representation as list of lists. The is equivalent but slightly more readable code:

>>> fromList [2,3,5,1,3,6,0,5,4,2,1,3] :: Matrix Four Three Int [[2,3,5],[1,3,6],[0,5,4],[2,1,3]]

Analogously

>>> fromList [7,3,-6] :: Tensor (Three :|: Nil) Int [7,3,-6]

and

>>> fromList [7,3,-6] :: Vector Three Int [7,3,-6]

are the same. In order to access an entry of a @'Data.Tensor.Tensor'@ we use the @'Data.Tensor.!'@ operator, which takes the same @'Data.TypeList.MultiIndex.MultiIndex'@ of the @'Data.Tensor.Tensor'@ as its second argument:

>>> let a = fromList [2,3,5,1,3,6,0,5,4,2,1,3] :: Matrix Four Three Int >>> let b = fromList [7,3,-6] :: Vector Three Int >>> a ! (toMultiIndex [1,3] :: (Four :|: (Three :|: Nil))) 5 >>> b ! (toMultiIndex [2] :: (Three :|: Nil)) 3

it returns the element at the coordinate (1,3) of the matrix @a@, and the element at the coordinate 2 of the vector b. In fact, thanks to type inference, we could simply write

>>> a ! toMultiIndex [1,3] 5 >>> b ! toMultiIndex [2] 2

And now a couple of examples of algebraic operations (requires adding "Data.Tensor.LinearAlgebra.Vector" to the import list):

>>> :m Data.Ordinal Data.TypeList.MultiIndex Data.Tensor.Vector Data.Tensor.LinearAlgebra.Vector >>> let a = fromList [2,3,5,1,3,6,0,5,4,2,1,3] :: Matrix Four Three Int >>> let b = fromList [7,3,-6] :: Vector Three Int >>> a .*. b [-7,-20,-9,-1]

is the product of matrix @a@ and vector @b@, while

>>> let c = fromList [3,4,0,-1,4,5,6,2,1] :: Matrix Three Three Int >>> c [[3,4,0],[-1,4,5],[6,2,1]] >>> charPoly c [106,13,8]

gives the coefficients of the characteristic polynomial of the matrix @c@.

## Properties

Versions | 0.1, 0.1.1, 0.2.0, 0.3.0, 0.3.0.1 |
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Dependencies | base (==4.*), vector [details] |

License | GPL-3 |

Author | Federico Squartini, Nicola Squartini |

Maintainer | Nicola Squartini <tensor5@gmail.com> |

Stability | experimental |

Category | Data, Math |

Uploaded | Wed Jun 13 20:09:36 UTC 2012 by NicolaSquartini |

Distributions | Debian:1.0.0.1, NixOS:0.3.0.1 |

Downloads | 986 total (15 in the last 30 days) |

Votes | |

Status | Docs uploaded by user Build status unknown [no reports yet] |

## Downloads

- tensor-0.1.tar.gz [browse] (Cabal source package)
- Package description (included in the package)