Marcus P S marcusps

Cython example of exposing C-computed arrays in Python without data copies

The goal of this example is to show how an existing C codebase for numerical computing (here c_code.c) can be wrapped in Cython to be exposed in Python.

The meat of the example is that the data is allocated in C, but exposed in Python without a copy using the PyArray_SimpleNewFromData numpy

	In this gist we will first show that we can beat the arc challenge
	(http://www.paulgraham.com/arcchallenge.html), and then build the library that
	shows how we did it. This gist is Literate Haskell and is of course executable. The packages needed are happstack-server and applicative-extras, installable using cabal.

	Let's start with some imports (for now, you can ignore these)

	> {-# LANGUAGE GADTs, TypeSynonymInstances #-}
	> module ArcChallenge where
	>
	> import Control.Applicative

	#!/usr/bin/env python
	"""
	Draws Hinton diagrams using matplotlib ( http://matplotlib.sf.net/ ).
	Hinton diagrams are a handy way of visualizing weight matrices, using
	colour to denote sign and area to denote magnitude.

	By David Warde-Farley -- user AT cs dot toronto dot edu (user = dwf)
	with thanks to Geoffrey Hinton for providing the MATLAB code off of
	which this is modeled.

	#!/usr/bin/env groovy

	@Grab(group='commons-lang', module='commons-lang', version='2.5')
	@Grab(group='net.sf.ezmorph', module='ezmorph', version='1.0.6')
	@Grab(group='commons-collections', module='commons-collections', version='3.2.1')
	@Grab(group='commons-beanutils', module='commons-beanutils', version='1.8.3')
	@Grab('net.sf.json-lib:json-lib:2.3-jdk15')
	import net.sf.json.*

	def cli = new CliBuilder(usage:'del2scrumptious.groovy')

	### MATPLOTLIBRC FORMAT

	# This is a sample matplotlib configuration file - you can find a copy
	# of it on your system in
	# site-packages/matplotlib/mpl-data/matplotlibrc. If you edit it
	# there, please note that it will be overridden in your next install.
	# If you want to keep a permanent local copy that will not be
	# over-written, place it in HOME/.matplotlib/matplotlibrc (unix/linux
	# like systems) and C:\Documents and Settings\yourname\.matplotlib
	# (win32 systems).

	"""
	Visualize points on the 3-simplex (eg, the parameters of a
	3-dimensional multinomial distributions) as a scatter plot
	contained within a 2D triangle.

	David Andrzejewski (david.andrzej@gmail.com)
	"""
	import numpy as NP
	import matplotlib.pyplot as P
	import matplotlib.ticker as MT

	#!/usr/bin/env ruby
	#
	# This script is a wrapper around pandoc that uses pandoc's
	# builtin citeproc support to generate a markdown bibliography
	# from bibtex.
	#
	# Inspired by Jacob Barney's [bib2mkd][] script.
	#
	# [bib2mkd]: http://jmbarney.dyndns.org/?/linux/bib2mkd/
	#

	<html>
	<body>
	<h1>Our Navigation</h1>
	<p>I'm writing an example xhtml document to get converted into markdown!</p>
	<h2>Examples</h2>

	<h3>Text formatting</h3>
	<p>Sometimes with longer <em>paragraphs</em><br/>we just want a new line <strong>immediately</strong>.</p>
	<div>Divs are block elements too, and people don't always put their text in p tags.</div>

	(use '[clojure.core.match :only [match]])

	(defn evaluate [env [sym x y]]
	(match [sym]
	['Number] x
	['Add] (+ (evaluate env x) (evaluate env y))
	['Multiply] (* (evaluate env x) (evaluate env y))
	['Variable] (env x)))

	(def environment {"a" 3, "b" 4, "c" 5})