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% Tutorial slides on Python.

%

% Author: Prabhu Ramachandran <prabhu at aero.iitb.ac.in>

% Copyright (c) 2005-2008, Prabhu Ramachandran

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% Title page

\title[Basic Python]{Python,\\a great programming toolkit:\\

numerics and plotting}

\author[Asokan \& Prabhu] {Asokan Pichai\\Prabhu Ramachandran}

\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}

\date[] {26, July 2009}

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  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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    \frametitle{Outline}

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\begin{frame}

  {Acknowledgements}

  \begin{center}

  This program is conducted by\\

  IIT, Bombay\\

  through CDEEP\\

  as part of  the open source initiatives\\

  under the aegis of\\

  \alert{National Mission on Education through ICT,} \\

  Ministry of HRD.

  \end{center}

\end{frame}

\begin{frame}

  \frametitle{Outline}

  \tableofcontents

  % You might wish to add the option [pausesections]

\end{frame}

\begin{frame}{Goal of the Workshop}

        At the end of this program, successful participants will be able

        to use python as their scripting and problem solving language.

        Aimed at Engg. students--focus on basic numerics and plotting--

        but should serve a similar purpose for others.\\

        At the minimum you will be able to use Python for your plotting immediately.

\end{frame}

\begin{frame}{Checklist}

  \begin{description}

	\item[pylab] matplotlib interface 

	\item[numpy] Array computing

        \item[scipy] numerical work

        \item[mayavi] \typ{enthought.mayavi}: 3D viz.

  \end{description}

\end{frame}

\section{30000 feet view}

\begin{frame}{Lets see what we can do!}

  \huge

  Hold on to your seatbelts

\end{frame}

\begin{frame}

  {That was done by\ldots}

  \begin{description}[CalisthenicsIsAnArt]

      \item[Arrays] 2--3 lines; 5 minutes to learn

      \item[2D plots] 5 lines; 10 minutes to learn

      \item[Simple 3D plots] 5 lines; 10 minutes to learn; GUI

          exploration!

      \item[Complex plots] relatively short (10-15 lines); more time to master; 

  \end{description}

  \inctime{15}

\end{frame}

\section{Matplotlib}

\subsection{Basic \typ{numpy} }

\newcommand{\num}{\texttt{numpy}}

\begin{frame}

  \frametitle{The \num\ module}

  \begin{itemize}

      \item Why?

  \item What:

    \begin{itemize}

    \item An efficient and powerful array type for various common data

      types

    \item Abstracts out the most commonly used standard operations on

      arrays

    \end{itemize}

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Examples of \num}

\begin{lstlisting}

# Simple array math example

>>> from numpy import *

>>> a = array([1,2,3,4])

>>> b = array([2,3,4,5])

>>> a*2 + b + 1 # Basic math!

array([5, 8, 11, 14])

# Pi and e are defined.

>>> x = linspace(0.0, 10.0, 1000)

>>> x *= 2*pi/10 # inplace.

# apply functions to array.

>>> y = sin(x)

\end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Basic concepts}

  \begin{itemize}

  \item fixed size (\typ{arr.size});

  \item Same type (\typ{arr.dtype}) of data

  \item arbitrary dimensionality

  \item \typ{arr.shape}: size in each dimension

  \item \alert{Note:} \typ{len(arr) != arr.size} in general

  \item \alert{Note:} By default array operations are performed

    \alert{elementwise}

  \item Indices, slicing: just like lists 

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{More examples of \num}

\vspace*{-8pt}

\begin{lstlisting}

>>> x = array([1., 2, 3, 4])

>>> size(x)

4

>>> x.dtype # What is a.dtype?

dtype('float64')

>>> x.shape

(4,)

>>> print rank(x), x.itemsize

1 8

>>> x[0] = 10

>>> print x[0], x[-1]

10.0 4.0

\end{lstlisting}

\inctime{10}

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\subsection{Plotting with \typ{pylab}}

\begin{frame}

    {IPython's \typ{pylab} mode}

\begin{itemize}

    \item \typ{pylab}: convenient 2D plotting interface to MPL

    \item Immediate use: \typ{ipython -pylab}

    \item Imports all of pylab for you!

    \item Allows for interactive plotting

\end{itemize}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Basic 2D plotting}

\begin{lstlisting}

>>> x = linspace(0, 2*pi, 1000)

>>> plot(x, sin(x)) 

>>> plot(x, sin(x), 'ro')

>>> xlabel(r'$\chi$', color='g')

# LaTeX markup!

>>> ylabel(r'sin($\chi$)', color='r')

>>> title('Simple figure', fontsize=20)

>>> savefig('/tmp/test.eps')

\end{lstlisting}

\begin{itemize}

  \item Also: PNG, PDF, PS, EPS, SVG, PDF

\end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Basic plotting \ldots}

\begin{lstlisting}

# Set properties of objects:

>>> l, = plot(x, sin(x))

# Why "l,"?

>>> setp(l, linewidth=2.0, color='r')

>>> l.set_linewidth(2.0)

>>> draw() # Redraw.

>>> setp(l) # Print properties

>>> clf() # Clear figure.

>>> close() # Close figure.

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Multiple figures}

\begin{lstlisting}

>>> figure(1)

>>> plot(x, sin(x))

>>> figure(2)

>>> plot(x, tanh(x))

>>> figure(1)

>>> title('Easy as 1,2,3')

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Legends and Annotation}

\begin{lstlisting}

>>> plot(x, cos(5*x), 'r--', 

         label='cosine')

>>> plot(x, sin(5*x), 'g--', 

         label='sine')

>>> legend() 

# Or use:

>>> legend(['cosine', 'sine'])

# Annotation:

>>> text(1,0, '(1,0)')

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    \frametitle{More commands \ldots}

    \begin{lstlisting}

# semilog, loglog 

>>> x = 10.**(-arange(100)*0.1)

>>> semilogx(x, x)

>>> semilogy(x, x)

>>> loglog(x, x)

>>> loglog(x, x*x)

    \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    \frametitle{More plots \ldots}

    \begin{lstlisting}

>>> clf()

>>> t = arange(0.1, 4, 0.1)

>>> s = exp(-t)

>>> e = 0.1*abs(randn(len(s)))

>>> errorbar(t, s, e)

# Scatter plots

>>> clf()

>>> t = randn(len(e))

>>> scatter(t, e, c=s)

    \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Note: \typ{pylab} in Python scripts}

\begin{lstlisting}

import pylab

x = pylab.linspace(0, 20, 1000)

pylab.plot(x, pylab.sin(x))

# Can also use:

from pylab import linspace, sin, plot

\end{lstlisting}

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{frame}[fragile]

  \frametitle{X-Y plot}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.5in}

    \includegraphics[height=2in, interpolate=true]{data/xyplot}

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

t1 = arange(0.0, 5.0, 0.1)

t2 = arange(0.0, 5.0, 0.02)

t3 = arange(0.0, 2.0, 0.01)

subplot(211)

plot(t1, cos(2*pi*t1)*exp(-t1), 'bo', 

     t2, cos(2*pi*t2)*exp(-t2), 'k')

grid(True)

title('A tale of 2 subplots')

ylabel('Damped')

subplot(212)

plot(t3, cos(2*pi*t3), 'r--')

grid(True)

xlabel('time (s)')

ylabel('Undamped')

\end{lstlisting}

    \end{block}

  \end{columns}

\end{frame}

\begin{frame}[fragile] \frametitle{Semi-log and log-log plots}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.5in}

  \includegraphics[height=2in, interpolate=true]{data/log}  

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

dt = 0.01

t = arange(dt, 20.0, dt)

subplot(311)

semilogy(t, exp(-t/5.0))

ylabel('semilogy')

grid(True)

subplot(312)

semilogx(t, sin(2*pi*t))

ylabel('semilogx')

grid(True)

# minor grid on too

gca().xaxis.grid(True, which='minor')  

subplot(313)

loglog(t, 20*exp(-t/10.0), basex=4)

grid(True)

ylabel('loglog base 4 on x')

\end{lstlisting}

  \end{block}

\end{columns}

\end{frame}

\begin{frame}[fragile] \frametitle{Errorbar}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.5in}

  \includegraphics[height=2in, interpolate=true]{data/errorbar}  

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

t = arange(0.1, 4, 0.1)

s = exp(-t)

e = 0.1*abs(randn(len(s)))

f = 0.1*abs(randn(len(s)))

g = 2*e

h = 2*f

errorbar(t, s, [e,g], f, fmt='o')

xlabel('Distance (m)')

ylabel('Height (m)')

title('Mean and standard error '\

      'as a function of distance')

\end{lstlisting}

  \end{block}

\end{columns}

\end{frame}

\begin{frame}[fragile] \frametitle{Histogram}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.5in}

  \includegraphics[height=2in, interpolate=true]{data/histogram}  

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

mu, sigma = 100, 15

x = mu + sigma*randn(10000)

# the histogram of the data

n, bins, patches = hist(x, 100, normed=1)

# add a 'best fit' line

y = normpdf( bins, mu, sigma)

l = plot(bins, y, 'r--', linewidth=2)

xlim(40, 160)

xlabel('Smarts')

ylabel('P')

title(r'$\rm{IQ:}\/ \mu=100,\/ \sigma=15$')

\end{lstlisting}

  \end{block}

\end{columns}

\end{frame}

\begin{frame}[fragile] \frametitle{Bar charts}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.5in}

  \includegraphics[height=2in, interpolate=true]{data/barchart}  

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

N = 5

menMeans = (20, 35, 30, 35, 27)

menStd =   ( 2,  3,  4,  1,  2)

# the x locations for the groups

ind = arange(N) 

# the width of the bars

width = 0.35       

p1 = bar(ind, menMeans, width, 

         color='r', yerr=menStd)

womenMeans = (25, 32, 34, 20, 25)

womenStd =   ( 3,  5,  2,  3,  3)

p2 = bar(ind+width, womenMeans, width, 

         color='y', yerr=womenStd)

ylabel('Scores')

title('Scores by group and gender')

xticks(ind+width, 

       ('G1', 'G2', 'G3', 'G4', 'G5'))

xlim(-width,len(ind))

yticks(arange(0,41,10))

legend((p1[0], p2[0]), 

       ('Men', 'Women'), shadow=True)

\end{lstlisting}

  \end{block}

\end{columns}

\end{frame}

\begin{frame}[fragile] \frametitle{Pie charts}

  \begin{columns}

    \column{0.5\textwidth}

    \hspace*{-0.4in}

  \includegraphics[height=2.0in, interpolate=true]{data/piechart}  

    \column{0.45\textwidth}

    \begin{block}{Example code}

    \tiny

\begin{lstlisting}

# make a square figure and axes

figure(1, figsize=(8,8))

ax = axes([0.1, 0.1, 0.8, 0.8])

labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'

fracs = [15,30,45, 10]

explode=(0, 0.05, 0, 0)