path: root/embellishing_a_plot/script.rst

.. Objectives
.. ----------

.. By the end of this tutorial you will be able to 

..  * Modify the attributes of the plot -- color, line style, linewidth
..  * Add a title to the plot with embedded LaTeX.
..  * Label x and y axes. 
..  * Add annotations to the plot. 
..  * Set and Get the limits of axes. 


.. Prerequisites
.. -------------

..   1. Using the ``plot`` command interactively
     
.. Author              : Nishanth Amuluru
   Internal Reviewer   : Anoop
   External Reviewer   :
   Language Reviewe    : Bhanukiran
   Checklist OK?       : <15-11-2010, Anand, OK> [2010-10-05]

Script
------

.. L1

{{{ Show the  first slide containing title, name of the production
team along with the logo of MHRD }}}

.. R1

Welcome to the tutorial on Embellishing Plots.


.. L2

{{{ Show the slide containing objectives }}}

.. R2

At the end of this tutorial, you will be able to, 

 1. Modify the attributes of the plot -- color, line style,linewidth.
 #. Add a title to the plot with embedded LaTeX.
 #. Label x and y axes. 
 #. Add annotations to the plot. 
 #. Set and Get the limits of axes.

.. R3

Let us start ipython with pylab loaded, open the terminal and type 
::
   
    ipython -pylab

.. L3

{{{ open the terminal and type ipython -pylab }}}

.. R4

We shall first make a simple plot and start decorating it.

.. L4

::
    
    x = linspace(-2, 4, 20)
    plot(x, sin(x))

.. R5

As we can see, the default colour and the default thickness of the
line is as decided by pylab. Wouldn't it be nice if we could control
these parameters in the plot? This is possible by passing additional
arguments to the plot command.
We shall first clear the figure and plot the same by passing the additional color
argument. Pass the argument 'r' for red color.

.. L5
     
::
   
    clf()
    plot(x, sin(x), 'r')

.. R6

The same plot is seen in red color.

.. L6

{{{Move the mouse pointer on the plot}}}

.. R7

The thickness of the line can be altered by 'linewidth' argument. 

.. L7
    
::
     
    plot(x, cos(x), linewidth=2)

.. R8

A plot with line thickness 2 is produced.

.. L8

{{{ Show the plot and compare the sine and cos plots }}}

.. R9

Pause the video and do this exercise. Resume the video, after the exercise is solved.

Plot sin(x) in blue colour and with linewidth as 3.

.. L9

{{{ Show slide with Question1 }}}

.. R10

A combination of colour and linewidth would do the job for us.

.. L10

::
    
    clf()
    plot(x, sin(x), 'b', linewidth=3)


.. R11 

To get the style of line as bunch of points not joined, pass the linestyle
argument with or without color argument.

.. L11
   
::
   
    clf()
    plot(x, sin(x), '.')

.. R12

We get a plot with only points.

.. L12
 
{{{Point at the dots on the plot}}}

.. R13

To get the same plot in blue colour.
 
.. L13
 
  ::
    clf()
    plot(x, sin(x), 'b.')

.. R14

Other available options for passing arguments can be seen in the 
documentation of plot.

.. L14
  
::
    
    plot?

{{{ Run through the documentation and show the options available }}}

{{{ Show the options available for line style and colors }}}


.. L15

{{{Show slide containing question 2}}}

.. R15

Pause the video and do this exercise. Resume the video, after the exercise is solved.

1. Plot the sine curve with green filled circles.
2. Plot the curve of x vs tan(x) in red dashed line and linewidth 3.


.. R16

For question 1, use a combination of linestyle and colour.

.. L16

{{{ Switch to terminal and type the following commands }}}  
::
    
    clf()
    plot(x, cos(x), 'go')

.. L17

For question 2, use a combination of linewidth argument and linestyle.

{{{ Switch to terminal and type the following commands }}}
::
   
    clf()
    plot(x, cos(x), 'r--')

.. R19

Now that we know how to produce a bare minimum plot with colour, style
and thickness of our interest, we shall look at further decorating the plot.

.. R20

Let us start with a plot for the function -x^2 + 4x - 5.

.. L20

::
   
    plot(x, -x*x + 4*x - 5, 'r', linewidth=2)

{{{ Show the plot window and switch back to terminal }}}

.. R21

As you can see, the figure does not have any description describing the plot.

To add a title to the plot to describe what the plot is, use the ``title`` command.

.. L21
  
::
   
    title("Parabolic function -x^2+4x-5")

The ``title`` command as you can see, takes a string as an argument 

{{{ Show the plot window and point to the title }}}

.. R22

The figure now has a title. But it is not formatted and does not look clean.

It would look shabby if there were fractions and more complex functions
like log and exp. Wouldn't it be good if the title is seen in LaTeX like formatting?

This is possible by adding a ``$`` sign before and after the part of the 
string that should be in LaTeX style.

.. L22
  
::
    
    title("Parabolic function $-x^2+4x-5$")

.. R23

As we can see, the polynomial is now formatted.

.. L23

{{{ Point at the polynomial }}}

.. L24

{{{Show slide containing question 4}}}

Pause the video and do this exercise. Resume the video, after the exercise is solved.

.. R24

{{{ Let us try out the following exercise }}}

Change the title of the figure such that the whole title is formatted
in LaTeX style.

.. R25

The solution is to enclose the whole string in between $. 

.. L25
  
::
    
    title("$Parabolic function -x^2+4x-5$")

.. R26

Although we have title, the plot is not complete without labelling x
and y axes. we shall label x-axis to "x" and y-axis to "f(x)".

.. L26
 
::
    
    xlabel("x")
    ylabel("f(x)")

.. L27



.. R27

As you can see, ``xlabel`` and 'ylabel' command takes a string as an argument. 
xlabel sets the label to x-axis as 'x' and ylabel sets the name to the y-axis as 'f(x)'.

.. R28



.. L28

::
    

{{{ Show the plot window and point to xlabel and ylabel and switch back to the terminal }}}

.. L29

{{{Show slide containing question 5}}}

.. R29

Pause the video and do this exercise. Resume the video, after the exercise is solved.

Set the x and y labels as "x" and "f(x)" in LaTeX style.

{{{ Pause for some time and then Show slide with answer 5 }}}

Since we need LaTeX style formatting, all we have to do is enclose the string
in between two $. 

.. L30



.. R30

{{{ Read out the commands on the slides }}}

    xlabel("$x$")
    ylabel("$f(x)$")

.. L31

{{{ Show the plot window with clean labels }}}

.. R31

The plot is now almost complete. Except that the points are not named. 
For example the point (2, -1) is the local maxima. We would
like to name the point accordingly. To do this use the function ``annotate``.

.. L31

{{{ Switch to terminal }}}
   
::
    
    annotate("local maxima", xy=(2, -1))

{{{ Show the annotation that has appeared on the plot }}}

.. R32

As you can see, the first argument to ``annotate`` command is the name we would
like to mark the point as, and the second argument is the co-ordinates of the
point at which the name should appear. It is a tuple containing two numbers.
The first is x co-ordinate and second is y co-ordinate.

.. L32

{{{ Point at the annotate command while explaining}}}

.. R33

Pause the video and do this exercise. Resume the video, after the exercise is solved.

Make an annotation called "root" at the point (-4, 0).
What happens to the first annotation ?

.. L33

{{{Show slide containing question 6}}}

.. L34

{{{Show slide with answer 6}}}
{{{ Switch to the terminal and type the command }}}
::

    annotate("root", xy=(-4,0))  

.. R34

As we can see, every annotate command makes a new annotation on the figure.

Now we have everything we need to decorate a plot, but the plot would be
incomplete if we can not set the limits of axes. This can be done using the
button provided on the plot window.

Else limits also can be get and set from the terminal. 
Use "xlim()" and "ylim()" functions to get the limits.

.. L35
  
::
   
    xlim()
    ylim()

.. R35

``xlim`` function returns the current x axis limits and ``ylim``
function returns the current y-axis limits.

Set the limits of x-axis from -4 to 5 by giving command xlim(-4,5).

.. L36

::
    
    xlim(-4, 5)

.. R36

.. R37

Similarly set the limits of y-axis appropriately.

.. L37

::
     
    ylim(-15, 2)


.. L38

{{{ Pause here and try out the following exercises }}}

Pause the video and do this exercise. Resume the video, after the exercise is solved.

{{{Show slide containing question 7 and read it out }}}

Set the limits of axes such that the area of interest is the rectangle (-1, -15) and (3, 0)

{{{ continue from paused state }}}

.. R38

As we can see, the lower and upper limits of x-axis in the question are -1 and 3 respectively.
The lower and upper limits of y-axis are -15 and 0 respectively.

.. L39

{{{Show slide with answer 7}}}

::

    xlim(-1, 3)
    ylim(-15, 0)

.. R39

This gives us the required rectangle.

.. L40

{{{ Show summary slide }}}

.. R40

Lets Summarize. In this spoken tutorial we have learnt, 

 1. to Modify the attributes of plot like color, line width, line style by passing additional arguments.
 #. to add title to a plot using 'title' command.
 #. to incorporate LaTeX style formatting by adding a ``$`` sign before and after the part of the 
string.
 #. to label x and y axes using xlabel() and ylabel() commands.
 #. to add annotations to a plot using annotate() command.
 #. to get and set the limits of axes using xlim() and ylim() commands.

.. L41

{{{ Show the 'self assesment questions' slide}}}

.. R41

Here are some self assessment questions for you to solve.

1. Draw a plot of cosine graph between -2pi to 2pi with line thickness 4.

2. Read thorugh the documentation and find out is there a way to modify the
   alignment of text in the command ``ylabel``.

   - Yes
   - No

  
3. How do you set the title as x^2-5x+6 in LaTex style formatting.

    
.. L42

{{{ solutions for the self assessment questions }}}

.. R42

And the answers,

1. In order to plot a cosine graph between the points -2pi and 2pi with line thickness 3,we use
the ``linspace`` and ``plot`` command as,
::
        
    x = linspace(-2*pi, 2*pi)
    plot(x, cos(x), linewidth=4)

2. No. We do not have an option to modify the alignment of text in the command ``ylabel``.

3. To set the title in LaTex style formatting,we write the equation between two dollar signs as,
::

    title("$x^2-5x+6$")


.. L43

{{{ a thank you slide }}}

.. R43

Hope you have enjoyed and found it useful.
Thankyou!