plotting-data/script.rst
author Amit Sethi
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.. Objectives
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.. ----------
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.. By the end of this tutorial, you will be able to
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.. 1. Defining a list of numbers
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.. 2. Squaring a list of numbers
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.. 3. Plotting data points.
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.. 4. Plotting errorbars.
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.. Prerequisites
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.. -------------
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..   1. getting started with plotting
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.. Author              : Amit 
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   Internal Reviewer   : Anoop Jacob Thomas<anoop@fossee.in> 
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   External Reviewer   :
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   Checklist OK?       : <put date stamp here, if OK> [2010-10-05]
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.. #[[Anoop: Add quickref]]
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.. #[[Anoop: Slides are incomplete, add summary slide, thank you slide
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   etc.]]
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===============================
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Plotting   Experimental  Data  
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===============================   
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{{{ Show the slide containing title }}}
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Hello  and welcome , this tutorial on  Plotting Experimental data is 
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presented by the fossee  team.  
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{{{ Show the Outline Slide }}}
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.. #[[Anoop: outline slide is missing]]
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Here  we will discuss plotting  Experimental data. 
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1. We will see how we can represent a sequence of numbers in Python. 
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2. We will also become familiar with  elementwise squaring of such a
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sequence. 
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3. How to plot data points using python.
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4. We will also see how we can use our graph to indicate Error.
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One needs   to  be  familiar  with  the   concepts  of  plotting
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mathematical functions in Python.
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We will use  data from a Simple Pendulum Experiment to illustrate. 
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.. #[[Anoop: what do you mean by points here? if you mean the
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   points/numbered list in outline slide, then remove the usage point
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   from here.]]
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{{{ Simple Pendulum data Slide }}} 
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.. #[[Anoop: slides are incomplete, work on slides and context
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   switches]]
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As we know for a simple pendulum length,L is directly  proportional to 
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the square of time,T. We shall be plotting L and T^2 values.
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First  we will have  to initiate L and  T values. We initiate them as sequence 
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of values.  We define a sequence by comma seperated values inside two square brackets.  
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This is also  called List.Lets create two sequences L and t.
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.. #[[Anoop: instead of saying "to tell ipython a sequence of values"
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   and make it complicated, we can tell, we define a sequence as]]
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.. #[[Anoop: sentence is incomplete, can be removed]]
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{{{ Show the initializing L&T slide }}}
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Type in ipython shell ::
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    L = [0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9]
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    t= [0.69, 0.90, 1.19,1.30, 1.47, 1.58, 1.77, 1.83, 1.94]
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To obtain the square of sequence t we will use the function square
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with argument t.This is saved into the variable tsquare.::
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   tsquare=square(t)
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   tsqaure
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   array([  0.4761, 0.81 , 1.4161,  1.69 , 2.1609,  2.4964, 3.1329, 
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   3.3489, 3.7636])
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.. #[[Anoop: how do you get the array([ 0.4761 ....]) output?]]
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Now to plot L vs T^2 we will simply type ::
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  plot(L,tsquare,'.')
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.. #[[Anoop: be consistent with the spacing and all.]]
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'.' here represents to plot use small dots for the point. ::
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  clf()
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You can also specify 'o' for big dots.::
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  plot(L,tsquare,'o')
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  clf()
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.. #[[Anoop: Make sure code is correct, corrected plot(L,t,o) to
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   plot(L,t,'o')]]
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.. #[[Anoop: again slides are incomplete.]]
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For any experimental there is always an error in measurements due to
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instrumental and human constaraints.Now we shall try and take into
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account error into our plots . The Error values for L and T are on
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your screen.We shall again intialize the sequence values in the same
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manner as we did for L and t
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The error data we will use is on your screen.
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{{{ Show the Adding Error Slide }}}
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.. #[[Anoop: give introduction to error and say what we are going to
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   do]]
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::
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    delta_L= [0.08,0.09,0.07,0.05,0.06,0.00,0.06,0.06,0.01]
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    delta_T= [0.04,0.08,0.03,0.05,0.03,0.03,0.04,0.07,0.08]
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Now to plot L vs T^2 with an error bar we use the function errorbar()
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The syntax of the command is as given on the screen. ::
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    errorbar(L,tsquare,xerr=delta_L, yerr=delta_T, fmt='b.')
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This gives a plot with error bar for x and y axis. The dots are of
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blue color. The parameters xerr and yerr are error on x and y axis and
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fmt is the format of the plot.
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similarly we can draw the same error bar with big red dots just change
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the parameters to fmt to 'ro'. ::
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    clf()
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    errorbar(L,tsquare,xerr=delta_L, yerr=delta_T, fmt='ro')
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thats it. you can explore other options to errorbar using the documentation 
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of errorbar.::
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   errorbar?
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{{{ Show Summary Slide }}}
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In this tutorial we have learnt : 
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1. How to declare a sequence of numbers.
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2. Plotting experimental data.
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3. The various options available for plotting dots instead of lines.
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4. Plotting experimental data such that we can also represent error. 
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 {{{ Show the "sponsored by FOSSEE" slide }}}
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.. #[[Anoop: again slides are incomplete]]
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This tutorial was created as a part of FOSSEE project.
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Hope you have enjoyed and found it useful.
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Thank You!
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