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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 group] {FOSSEE}

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

\date[] {SciPy.in 2010, Tutorials}

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%% the beginning of each subsection:

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  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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{

  \begin{frame}<beamer>

    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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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[interpolate=true,width=2.35in]{data/stline_dots.png}

\includegraphics[interpolate=true,width=2.35in]{data/stline_points.png}

\end{figure}

\end{frame}

\begin{frame}[fragile]

\frametitle{Additional Line Styles}

\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: Appending elements}

\begin{lstlisting}

In []: p.append(11)

In []: p

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

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

In []: p.append(b)

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

\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 & 0.69 & \\ \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}

Our data is present in \typ{pendulum.txt}. Let's look at it.

\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{Looking at \typ{pendulum.txt}}

\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

\begin{itemize}

  \item File contains L vs.\ T values 

  \item First Column -- L values

  \item Second Column -- T values

\end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{\typ{loadtxt}}

  \begin{itemize}

  \item We shall use the \typ{loadtxt} command to load data

  \item Let's use \typ{primes.txt} file learn to use it

  \item \typ{primes.txt} has a single column

  \item Then, we shall use it for \typ{pendulum.txt} -- 2 cols

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

\frametitle{What's in \typ{primes.txt}?}

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

\begin{lstlisting} 

In []: cat primes.txt 

2

3      

5      

7     

11     

13

.

.

.

\end{lstlisting}  %$

\end{frame}

\begin{frame}[fragile]

  \frametitle{\typ{loadtxt} \ldots}

  \begin{lstlisting}

In []: primes = loadtxt('primes.txt')

In []: primes

Out[]: array([ 2., 3., 5., 7., 11., 13., 

               17., 19., 23., 29., 31., 

               37., 41., 43., 47., 53., 

               59., 61., 67., 71., 73., 

               79., 83., 89., 97.])

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

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

  \begin{lstlisting}

In []: pend = loadtxt('pendulum.txt')

In []: pend

  \end{lstlisting}

  \begin{itemize}

  \item \typ{pend} is 2 Dimensional. 

  \item We don't \alert{yet} know how to handle it.

  \item We obtain 1D sequences using \typ{unpack=True}

  \end{itemize}

  \begin{lstlisting}

In []: L, T = loadtxt('pendulum.txt', 

                      unpack=True)

In []: print L, T

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

Out[]: 90 90

  \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)

 ....:

 ....:

\end{lstlisting}

\alert{Hit ``ENTER'' key twice, to get out of \typ{for} loop}.

\begin{lstlisting}

In []: print len(tsq)

Out[]: 90

\end{lstlisting}

\typ{tsq} is a \kwrd{list} of squares of \typ{T} values.

\end{frame}

\begin{frame}[fragile]

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

\begin{lstlisting}

In []: plot(L, tsq, '.')

\end{lstlisting}

\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 Plot attributes and plotting points

  \item Lists

  \item \kwrd{for}

  \item Loading data from files

\end{itemize}

\end{frame}

\end{document}

%% Questions for Quiz %%

%% ------------------ %%

\begin{frame}[fragile]

\frametitle{\incqno }

  \begin{lstlisting}

  In []: a = [1, 2, 5, 9]

  In []: a[0:-1]

  \end{lstlisting}

  What is the output?

\end{frame}

\begin{frame}

\frametitle{\incqno }

  How do you combine two lists \emph{a} and \emph{b} to produce one list?

\end{frame}

\begin{frame}[fragile]

\frametitle{\incqno }

  \begin{lstlisting}

  In []: a = [1, 2, 5, 9]

  \end{lstlisting}

  How do you add the value 10 to the end of this list?

\end{frame}

\begin{frame}

\frametitle{\incqno }

Write the code to read a file \texttt{data.txt} and print each line of it?

\end{frame}

\begin{frame}[fragile]

\frametitle{\incqno }

What would be the result of the following code snippet:

\begin{lstlisting}

In []: x = linspace(0, 10, 50)

In []: y = linspace(50, 100, 100)

In []: plot(x, y)

\end{lstlisting}

\end{frame}

\begin{frame}[fragile]

\frametitle{\incqno }

The following code snippet has an error/bug:

\begin{lstlisting}

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

In []: t = [0.69, 0.90, 1.19, 1.30]

In []: tsq = []

In []: for time in t:

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

 ....:     plot(l, tsq)

\end{lstlisting}

What is the error? How do you fix it?

\end{frame}