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%Tutorial slides on Python.

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% Author: FOSSEE

% Copyright (c) 2009, FOSSEE, IIT Bombay

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% Title page

\title[Plotting with Python]{Python for Science and Engg: Plotting experimental data}

\author[FOSSEE] {FOSSEE}

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

\date[] {7 November, 2009\\Day 1, Session 2}

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%% the beginning of each subsection:

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    \frametitle{Outline}

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    \frametitle{Outline}

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% DOCUMENT STARTS

\begin{document}

\begin{frame}

  \titlepage

\end{frame}

\begin{frame}

  \frametitle{Outline}

  \tableofcontents

  % You might wish to add the option [pausesections]

\end{frame}

%\begin{frame}

%\frametitle{Python Scripts\ldots}

%  \begin{itemize}

%    \item Open a new file in an \alert{editor}

%    \item Copy and paste from the output of \typ{\%hist -n}

%    \item Save the file as \typ{sine_plot.py}

%  \end{itemize}

%  \begin{itemize}

%  \item run the file in IPython using \typ{\%run -i sine_plot.py}\\

%  \end{itemize}

%\end{frame}

\section{Scripts}

\begin{frame}[fragile]

\frametitle{Python Scripts}

  \begin{itemize}

  \item four\_plot.py is called a Python Script

  \item run the file in IPython using \typ{\%run -i four_plot.py}

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Why would I plot f(x)?}

How often do we plot analytical functions?\\We plot experimental data more.

\begin{small}

\begin{lstlisting}

In []: x = [0, 1, 2, 3]

In []: y = [7, 11, 15, 19]

In []: plot(x, y)

Out[]: [<matplotlib.lines.Line2D object at 0xa73aa8c>]

In []: xlabel('X')

Out[]: <matplotlib.text.Text object at 0x986e9ac>

In []: ylabel('Y')

Out[]: <matplotlib.text.Text object at 0x98746ec>

\end{lstlisting}

\end{small}

\end{frame}

\begin{frame}[fragile]

\begin{figure}

\includegraphics[width=3.5in]{data/straightline.png}

\end{figure}

\alert{Is this what you have?}

\end{frame}

\begin{frame}[fragile]

\frametitle{Plotting points}

\begin{itemize}

\item What if we want to plot the points!

\end{itemize}

\begin{lstlisting}

  In []: clf()

  In []: plot(x, y, 'o')

  Out[]: [<matplotlib.lines.Line2D object at 0xac17e0c>]

  In []: clf()

  In []: plot(x, y, '.')

  Out[]: [<matplotlib.lines.Line2D object at 0xac17e0c>]

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\begin{figure}

\includegraphics[width=2in]{data/stline_dots.png}

\includegraphics[width=2in]{data/stline_points.png}

\end{figure}

\end{frame}

\begin{frame}[fragile]

\frametitle{Additional Plotting Attributes}

\begin{itemize}

  \item \kwrd{'o'} - Filled circles

  \item \kwrd{'.'} - Small Dots

  \item \kwrd{'-'} - Lines

  \item \kwrd{'- -'} - Dashed lines

\end{itemize}

\end{frame}

\section{Lists}

\begin{frame}[fragile]

  \frametitle{Lists: Introduction}

  \begin{lstlisting}

    In []: x = [0, 1, 2, 3]

    In []: y = [7, 11, 15, 19]

  \end{lstlisting}

What are \typ{x} and \typ{y}?\\

\begin{center}

\alert{\typ{lists!!}}

\end{center}

\end{frame}

\begin{frame}[fragile]

\frametitle{Lists: Initializing \& accessing elements}

\begin{lstlisting}

In []: mtlist = [] #Empty List

In []: a = [ 1, 2, 3, 4, 5] 

In []: a[0]+a[1]+a[-1]

Out[]: 8

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{List: Slicing}

  \begin{block}{Remember\ldots}

	\kwrd{In []: a = [ 1, 2, 3, 4, 5]}

  \end{block}

\begin{lstlisting}

In []: a[1:3]  # A slice.

Out[]: [2, 3]

In []: a[1:-1]

Out[]: [2, 3, 4]

\end{lstlisting}

\alert{\typ{list[initial:final]}}

\end{frame}

%% more on list slicing

\begin{frame}[fragile]

\frametitle{List operations}

\begin{lstlisting}

In []: b = [ 6, 7, 8, 9]

In []: c = a + b

In []: c

Out[]: [1, 2, 3, 4, 5, 6, 7, 8, 9]

In []: a.append(6)

In []: a

Out[]: [ 1, 2, 3, 4, 5, 6]

\end{lstlisting}

%\inctime{10}

\end{frame}

\section{Simple Pendulum}

\begin{frame}[fragile]

\frametitle{Simple Pendulum - L and T}

Let us look at the Simple Pendulum experiment.

\begin{center}

\begin{small}

\begin{tabular}{| c | c | c |}

\hline

$L$ & $T$ & $T^2$ \\ \hline

0.1 & 0.6900 & \\ \hline

0.2 & 0.8989 & \\ \hline

0.3 & 1.1867 & \\ \hline

0.4 & 1.2991 & \\ \hline

0.5 & 1.4656 & \\ \hline

0.6 & 1.5843 & \\ \hline

0.7 & 1.7706 & \\ \hline

0.8 & 1.8296 & \\ \hline

0.9 & 1.9440 & \\ \hline

\end{tabular}

\end{small}\\

\alert{$L \alpha T^2$}

\end{center}

\end{frame}

\begin{frame}[fragile]

\frametitle{Lets use lists}

\begin{lstlisting}

In []: l = [0.1, 0.2, 0.3, 0.4, 0.5, 

            0.6, 0.7, 0.8, 0.9]

In []: t = [0.69, 0.8989, 1.1867, 

            1.2991, 1.4656, 1.5843, 

            1.7706, 1.8296, 1.9440]

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Plotting $L$ vs $T^2$}

\begin{itemize}

\item We must square each of the values in \typ{t}

\item How to do it?

\item We use a \kwrd{for} loop to iterate over \typ{t}

\end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Plotting $L$ vs $T^2$}

\begin{lstlisting}

In []: tsq = []

In []: for time in t:

 ....:     tsq.append(time*time)

In []: plot(l, tsq)

Out[]: [<matplotlib.lines.Line2D object at 0xa5b05ac>]

\end{lstlisting}

This gives \kwrd{tsq} which is the list of squares of \typ{t} values.

\end{frame}

\begin{frame}[fragile]

  \frametitle{How to come out of the \textt{for} loop?}

  Hit the ``enter'' key twice to come to the previous indentation level

  \begin{lstlisting}

    In []: for time in t:

     ....:     tsq.append(time*time)

     ....:     

     ....:     

    In []:

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\begin{figure}

\includegraphics[width=3.5in]{data/L-TSq-limited.png}

\end{figure}

\end{frame}

\begin{frame}[fragile]

\frametitle{What about larger data sets?}

\alert{Data is usually present in a file!} \\

Lets look at the \typ{pendulum.txt} file.

\begin{lstlisting}

$ cat pendulum.txt 

1.0000e-01 6.9004e-01

1.1000e-01 6.9497e-01

1.2000e-01 7.4252e-01

1.3000e-01 7.5360e-01

1.4000e-01 8.3568e-01

1.5000e-01 8.6789e-01

\end{lstlisting}

\ldots

\begin{block}{Windows users:}

  >type pendulum.txt

\end{block}

\end{frame}

\begin{frame}[fragile]

\frametitle{Reading \typ{pendulum.txt}}

\begin{itemize}

  \item Let us generate a plot from the data file

  \item File contains L vs. T values 

  \item L - Column1; T - Column2

\end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{Plotting from \typ{pendulum.txt}}

Open a new script and type the following:

\begin{lstlisting}

l = []

t = []

for line in open('pendulum.txt'):

    points = line.split()

    l.append(float(points[0]))

    t.append(float(points[1]))

tsq = []

for time in t:

    tsq.append(time*time)

plot(l, tsq, '.')

\end{lstlisting}

\end{frame}

\begin{frame}

\frametitle{Save and run}

\begin{itemize}

  \item Save as pendulum\_plot.py.

  \item Run using \kwrd{\%run -i pendulum\_plot.py}

\end{itemize}

\end{frame}

\begin{frame}[fragile]

\begin{figure}

\includegraphics[width=3.5in]{data/L-Tsq.png}

\end{figure}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Reading files \ldots}

\typ{for line in open('pendulum.txt'):}

\begin{itemize}

\item opening file `\typ{pendulum.txt}'

\item reading the file line by line

\item \typ{line} is a \kwrd{string}

\end{itemize}

\end{frame}

\section{Strings}

\begin{frame}[fragile]

\frametitle{Strings}

Anything within ``quotes'' is a string!

\begin{lstlisting}

' This is a string '  

" This too! "

""" This one too! """

''' And one more! '''

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Strings and \typ{split()}}

  \begin{lstlisting}

In []: greet = 'hello world'

In []: greet.split()

Out[]: ['hello', 'world']

  \end{lstlisting}

This is what happens with \typ{line}

  \begin{lstlisting}

In []: line = '1.2000e-01 7.4252e-01'

In []: line.split()

Out[]: ['1.2000e-01', '7.4252e-01']

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Getting floats from strings}

  \begin{lstlisting}

In []: type(points[0])

Out[]: <type 'str'>

  \end{lstlisting}

But, we need floating point numbers

  \begin{lstlisting}

In []: t = float(points[0])

In []: type(t)

Out[]: <type 'float'>

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{Let's review the code}

\begin{lstlisting}

l = []

t = []

for line in open('pendulum.txt'):

    points = line.split()

    l.append(float(points[0]))

    t.append(float(points[1]))

tsq = []

for time in t:

    tsq.append(time*time)

plot(l, tsq, '.')

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\begin{figure}

\includegraphics[width=3.5in]{data/L-Tsq.png}

\end{figure}

\end{frame}

\section {Summary}

\begin{frame}[fragile]

\frametitle{What did we learn?}

\begin{itemize}

  \item Python scripts

  \item \kwrd{\%run -i}

  \item Plotting points

  \item Plot attributes

  \item Lists

  \item \kwrd{for}

  \item Reading files

  \item Strings