Python-3.4.3/C2/Plotting-Data/English

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Python/C2/Plotting data /English


Title of script: Plotting data

Author: Aditya Palaparthy

Keywords: Python, IPython, plot, title, errorbar, video tutorial

Visual Cue
Narration
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containing title, name of the production team along with the logo of MHRD

Hello Friends. Welcome to the tutorial on "Plotting data ".
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Objectives


In this tutorial, we will learn about
  • Define a list of numbers.
  • Perform element-wise squaring of the list.
  • Plot data points.
  • Plot errorbars.
System Requirements

Ubuntu Linux 14.04


To record this tutorial, I am using
  • Ubuntu Linux 14.04 operating system
  • Python 3.4.3
  • IPython 5.1.0
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Pre-requisites


To practise this tutorial, you should know how to
  • run basic Python commands on the ipython console
  • use Plots interactively
  • Embellish a plot

If not, see the relevant Python tutorials on this website.

[Terminal]

ipython3


Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.


Now, type ipython3 and press Enter.

[IPython console]

%pylab and press Enter.

Let us initialise the pylab package.


Type %pylab and press Enter.

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Example - Simple Pendulum

Let us see an example for plotting the data related to a Simple Pendulum.


For a simple pendulum L is directly proportional to the square of time T.


We will be plotting L and T square values.

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Simple Pendulum Data


Let us use the data shown here for plotting.
[Ipython Terminal]


l = [0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9]


t= [0.69, 0.90, 1.19,1.30, 1.47, 1.58, 1.77, 1.83, 1.94]

First let us initiate 'l' and 't' values.

We initiate them as sequence of values. This is also called as List.

Type

l equal to within square brackets values and press Enter

t equal to within square brackets the values and press Enter

[Ipython Terminal]

tsquare=square(t)


Now we will obtain square of t by using function square.

Type

tsquare=square within parentheses t and press Enter

tsquare Now type

tsquare and press Enter

show array in terminal


array([ 0.4761, 0.81 , 1.4161, 1.69 , 2.1609, 2.4964, 3.1329,

3.3489, 3.7636])

We see the values of array tsquare
[Ipython Terminal]


plot(l,tsquare,'.')


Now to plot L versus T square, we will simply type

plot within parentheses I comma tsquare comma within single quotes dot and press Enter

Show the plot window We see the required plot.
[Ipython Terminal]


clf()

You can also specify 'o' for filled circles.


For this let us clear the plot first.


Type clf parentheses Enter

Show plot window So the plot is clear now.
plot(l,tsquare,'o') Now type,

plot within parentheses I comma tsquare comma within single quotes o and press Enter

Show plot window We see the plot with filled circles.
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Exercise 1

Pause the video. Try this exercise and then resume the video.


Plot the given experimental data with large dots. The data is on your screen.

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Exercise 1 data

Use the error data given here for plotting.
[Ipython Terminal]


delta_l= [0.08,0.09,0.07,0.05,0.06,0.00,0.06,0.06,0.01]

delta_t= [0.04,0.08,0.03,0.05,0.03,0.03,0.04,0.07,0.08]

We shall again initialize the sequence values in the same manner as we did for l and t.


Type delta underscore l equal to within square bracket the values and press Enter

delta underscore t within square bracket the values and press Enter

[Ipython Terminal]


errorbar(l,tsquare,xerr=delta_l, yerr=delta_t, fmt='bo')


Now to plot L versus T square with an error bar, we use the function errorbar().

So type,

errorbar within parentheses I comma tsquare comma xerr equalto delta underscore I comma y underscore err equalto delta underscore t comma fmt equal to within single quotes bo

and press Enter

Show plot window We see plot L versus T square with an error bar.
[Ipython Terminal]


errorbar?

You can explore other options of errorbar using the documentation of errorbar.

That is, errorbar question mark

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Exercise 2


Pause the video. Try this exercise and then resume the video.


Plot the given experimental data with small dots.


Also include the error in your plot.

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Exercise 2 data

Use the data given here for plotting.
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Summary slide


This brings us to the end of this tutorial. In this tutorial, we have learned to,


  1. Declare a list of numbers using the function array.
  1. Perform element-wise squaring using the square function.
  2. Use the various options available for plotting like dots, lines.
  3. Plot experimental data such that we can also represent error by using the errorbar() function.
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Evaluation


Here are some self assessment questions for you to solve.


  1. Square the following sequence.distance underscore values equal to within square brackets 2.1,4.6,8.72,9.03
  2. Plot L versus T in red pluses.
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Solutions


And the answers,


1.To square a sequence of values, we use the function square. So

square within parentheses distance underscore values


Answer to the second question

2. We pass an additional argument stating the desired parameter

plot within parentheses L comma T comma within single quotes r plus for red pluses

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Forum

Please post your timed queries in this forum.
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Fossee Forum

Please post your general queries on Python in this forum.
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Textbook Companion

FOSSEE team coordinates the TBC project.
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Acknowledgement

Spoken-tutorial is funded by NMEICT, MHRD, Govt. of India.

For more details, visit this website.

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Thank You

This is underscore ________ from IIT Bombay signing off.

Thank You

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Pratham920