= Repa (REgular PArallel arrays) =

Repa provides high performance, regular, multi-dimensional, shape polymorphic parallel arrays.
All numeric data is stored unboxed. Functions written with the Repa combinators
are automatically parallel provided you supply +RTS -Nwhatever on the command
line when running the program. Repa means "turnip" in Russian. If you don't like turnips then this library probably isn't for you.

== Download ==
Repa is split up into a few packages to help control dependencies.

|| [http://hackage.haskell.org/package/repa repa] || The base library, defining the array type and combinators. ||
|| [http://hackage.haskell.org/package/repa-bytestring repa-bytestring] || Conversions to and from !ByteString. ||
|| [http://hackage.haskell.org/package/repa-io repa-io] || Reading and writing arrays in various formats, including BMP. ||
|| [http://hackage.haskell.org/package/repa-algorithms repa-algorithms] || Some reusable matrix algorithms. ||
|| [http://hackage.haskell.org/package/repa-devil repa-devil] || Bindings to the DevIL image library. ||
|| [http://hackage.haskell.org/package/repa-examples repa-examples] || Example applications. ||

If you want the lot then just install the examples, and this will pull down the rest.
{{{
cabal install repa-examples
}}}

== From the source repo ==
The darcs source repos are at [http://code.ouroborus.net/repa/]

== Frequently Asked Questions (FAQ) ==
Q: GHC complains:  `ghc.exe: could not execute opt`  what's up with that? [[br]]
A: `opt` is the LLVM optimiser. You need to install [http://llvm.org/ LLVM].

Q: Where do I ask further questions? [[br]]
A: Ask on [http://stackoverflow.com/search?q=repa Stack Overflow], or send a message to `repa@ouroborus.net` if that doesn't help.

== Report a bug ==
To report bugs, request features, or get an account on the trac, please send email to `repa@ouroborus.net`

== Papers and Tutorials ==

[http://www.cse.unsw.edu.au/~benl/papers/repa/repa-icfp2010.pdf Regular Shape Polymorphic Arrays in Haskell]
 * Describes the overall approach to fusion, and how the shape polymorphism works.
 * Since this paper was published, the internals have changed slightly, but the overall structure is the same.

[http://www.cse.unsw.edu.au/~benl/papers/stencil/stencil-icfp2011-sub.pdf Efficient Parallel Stencil Convolution in Haskell]
 * Describes the current array representation.
 * Discusses the back-end, how the parallelism works, and how to write fast code.
 * Describes Repa's special support for Stencil convolutions.

[http://www.haskell.org/haskellwiki/Numeric_Haskell:_A_Repa_Tutorial Tutorial on usage and optimisation]
 * Contains lots of simple examples to get you started.
 * High level discussion of fusion, optimisation, and how to use the {{{force}}} function.

== Examples ==
Here is the output of some of the examples included in the [http://hackage.haskell.org/package/repa-examples repa-examples] package:

 || fft2d-highpass || Laplace ||
 || [[Image(WikiStart:lena-high2-thumb.jpg)]] || [[Image(WikiStart:pls-400x400-out-thumb.jpg)]] ||
 || [wiki:Examples/Fft2dHighpass more info] || [wiki:Examples/Laplace more info] || 

== Demo ==
There is also an OSX demo that does edge detection on a video stream:
 
 || [[Image(WikiStart:beholder-thumb.jpg)]] ||
 || video: [http://code.ouroborus.net/beholder/video/Edge480.mov low(10MB)]  [http://code.ouroborus.net/beholder/video/Edge720.mov high(40MB)] || 

 * The [http://code.ouroborus.net/beholder/beholder-head/ source] should compile with XCode 3.2.1, GHC 7.0.3 and Repa 2.0.0, but you need to update and run the CONFIGURE.sh script to point it to your GHC install. 
 * There are also prebuilt OSX i386 versions for [http://code.ouroborus.net/beholder/distro/beholder-N2.tgz two] [http://code.ouroborus.net/beholder/distro/beholder-N4.tgz four] and [http://code.ouroborus.net/beholder/distro/beholder-N6.tgz six] threads. These just have the corresponding +RTS -N# option baked in, you can set it in the main.m module. Some day I will make it so you can select this from the GUI.
 * You can also run the edge detector over a single uncompressed .bmp file using the repa-canny program from the [http://hackage.haskell.org/package/repa-examples repa-examples] package.