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%Tutorial slides on Python.

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% Author: FOSSEE

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% Title page

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

\author[FOSSEE group] {FOSSEE}

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

\date[] {SciPy 2010, Introductory tutorials,\\Day 1, Session 2}

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%% the beginning of each subsection:

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    \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}

  \frametitle{Outline}

  \tableofcontents

  % You might wish to add the option [pausesections]

\end{frame}

\section{Plotting Points}

\begin{frame}[fragile]

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

Do we plot analytical functions or experimental data?

\begin{small}

\begin{lstlisting}

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

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

In []: plot(time,distance)

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

In []: xlabel('time')

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

In []: ylabel('distance')

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(time, distance, 'o')

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

  In []: clf()

  In []: plot(time, distance, '.')

  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 \typ{'o'} - Filled circles

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

  \item \typ{'-'} - Lines

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

\end{itemize}

\end{frame}

\section{Lists}

\begin{frame}[fragile]

  \frametitle{Lists: Introduction}

  \begin{lstlisting}

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

    In []: distance = [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 = [] 

\end{lstlisting}

\emphbar{Empty List}

\begin{lstlisting}

In []: p = [ 2, 3, 5, 7] 

In []: p[1]

Out[]: 3

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

Out[]: 12

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{List: Slicing}

  \begin{block}{Remember\ldots}

	\kwrd{In []: p = [ 2, 3, 5, 7]}

  \end{block}

\begin{lstlisting}

In []: p[1:3]

Out[]: [3, 5]

\end{lstlisting}

\emphbar{A slice}

\begin{lstlisting}

In []: p[0:-1]

Out[]: [2, 3, 5]

In []: p[::2]

Out[]: [2, 5]

\end{lstlisting}

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

\end{frame}

\begin{frame}[fragile]

  \frametitle{List: Slicing}

  What is the output of the following?

\begin{lstlisting}

In []: p[1::2]

In []: p[1:-1:2]

\end{lstlisting}

\end{frame}

%% more on list slicing

\begin{frame}[fragile]

\frametitle{List operations}

\begin{lstlisting}

In []: b = [ 11, 13, 17]

In []: c = p + b

In []: c

Out[]: [2, 3, 5, 7, 11, 13, 17]

In []: p.append(11)

In []: p

Out[]: [ 2, 3, 5, 7, 11]

\end{lstlisting}

Question: Does \typ{c} change now that \typ{p} is changed?

%\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 & 0.69 & \\ \hline

0.2 & 0.90 & \\ \hline

0.3 & 1.19 & \\ \hline

0.4 & 1.30 & \\ \hline

0.5 & 1.47 & \\ \hline

0.6 & 1.58 & \\ \hline

0.7 & 1.77 & \\ \hline

0.8 & 1.83 & \\ \hline

0.9 & 1.94 & \\ \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, 0.90, 1.19, 

            1.30, 1.47, 1.58, 

            1.77, 1.83, 1.94]

\end{lstlisting}

\alert{Gotcha}: Make sure \typ{L} and \typ{t} have the same number

of elements

\begin{lstlisting}

In []: print len(L), len(t)

\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 do we 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)

 ....:

 ....:

\end{lstlisting}

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

\begin{lstlisting}

In []: print len(L), len(t), len(tsq)

Out[]: 9 9 9

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{How do you exit the \texttt{for} loop?}

  Hitting the ``ENTER'' key twice returns the cursor to the previous indentation level

  \begin{lstlisting}

    In []: for time in t:

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

     ....:     

     ....:     

    In []: plot(L, tsq)

  \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} 

In []: 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

\end{lstlisting}  %$

\ldots

\end{frame}

\begin{frame}[fragile]

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

\begin{itemize}

  \item File contains L vs.\ T values 

  \item First Column - L values

  \item Second Column - T values

  \item Let us generate a plot from the data file

\end{itemize}

\end{frame}

\begin{frame}[fragile]

    \frametitle{Gotcha and an aside}

    Ensure you are in the same directory as \typ{pendulum.txt}\\

    if not, do the following on IPython:

    \begin{lstlisting}

In []: %cd directory_containing_file

# Check if pendulum.txt is there.

In []: ls

# Also try 

In []: !ls

    \end{lstlisting}

    \alert{Note:} \typ{\%cd} is an IPython magic command.  For more information

    do:

    \begin{lstlisting}

In []: ?

    \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

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

Open a new script and save as \typ{pendulum_plot.py}

\begin{lstlisting}

L = []

t = []

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

    point = line.split()

    L.append(float(point[0]))

    t.append(float(point[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 \typ{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}

Why so many?

\begin{lstlisting}

' "Do or do not.  No try." said Yoda.'  

" ' is a mighty lonely quote."

\end{lstlisting}

The triple quoted ones can span multiple lines!

\begin{lstlisting}

""" The quick brown

fox jumped over

    the lazy dingbat. 

"""

\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 = '1.20 7.42'

In []: point = line.split()

In []: point

Out[]: ['1.20', '7.42']

  \end{lstlisting}

\end{frame}