Hello friends and welcome to the tutorial on Embellishing Plots

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In this tutorial, we shall look at how to modify the colour, thickness and 

linestyle of the plot. We shall then learn how to add title to the plot and 

then look at adding labels to x and y axes. we shall also look at adding 

annotations to the plot.

Let us start ipython with pylab loaded, by typing

::

    ipython -pylab

on the terminal

{{{ shit to terminal and type ipython -pylab }}}

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

::

    x = linspace(-2, 4, 20)

    plot(x, sin(x))

As you can see, the colour and thickness of line as decided by pylab. It would

be nice if we could control these parameters in the plot. This is possible by

passing additional arguments to the plot command.

The second argument that we shall be passing is colour. We shall first clear

the figure and plot the same in red colour.Hence

::

    clf()

    plot(x, sin(x), 'r')

Plots the same curve but now in red colour.

To alter the thickness of the line, we use the =linewidth= argument in the plot

command.Hence

::

    plot(x, cos(x), linewidth=2)

produces a plot with a thicker line.

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

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

%% 1 %% Plot sin(x) in blue colour and with linewidth as 3

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

::

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

produces the required plot

#[Nishanth]: I could not think of a SIMPLE recipe approach for introducing

             linestyle. Hence the naive approach.

Occasionally we would also want to alter the style of line. Sometimes all we

want is just a bunch of points not joined. This is possible by passing the

linestyle argument along with or instead of the colour argument.Hence

::

    clf()

    plot(x, sin(x), '.')

produces a plot with only points.

To produce the same plot but now in blue colour, we do

::

    clf()

    plot(x, sin(x), 'b.')

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

::

    plot?

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

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

%% 2 %% Plot the sine curve with green filled circles.

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All we have to do is use a combination of linestyle and colour to acheive this.

Hence

::

    clf()

    plot(x, cos(x), 'go')

produces the required plot.

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

%% 3 %% Produce a plot of tangent curve with red dashed line and linewidth 3

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Now that we know how to produce a bare minimum plot with colour, style and

thickness of our interest, we shall look at decorating the plot.

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

::

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

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

We now have the plot in a colour and linewidth of our interest. As you can see,

the figure does have any description describing the plot.

We will now add a title to the plot by using the =title= command.

::

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

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

The figure now has a title which describes what the plot is.

The =title= command as you can see, takes a string as argument and set the

title accordingly.

The formatting in title is messed and it does not look clean. You can imagine

what would be the situation if there were fractions and more complex functions

like log and exp. Wouldn't it be good if there was LaTex like formatting.

That is also possible by adding a $ sign before and after the part of the 

string that should be LaTex style.

for instance, we can use

::

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

and we get the polynomial formatted properly.

#[Nishanth]: Unsure if I have to give this exercise since enclosing the whole

             string in LaTex style is not good

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

%% 4 %% Change the title of the figure such that the whole title is formatted

        in LaTex style

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

::

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

gives a title that looks neatly formatted.

Although we have title, the plot is not complete without labelling x and y

axes. Hence we shall label x-axis to "x" and y-axis to "f(x)"

::

    xlabel("x")

{{{ Switch to plot window and show the xlabel }}}

As you can see, =xlabel= command takes a string as argument, similar to the

=title= command and sets it to x-axis.

Similarly,

::

    ylabel("f(x)")

sets the name of y-axis as "f(x)"

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

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

%% 5 %% Set the x and y labels as "x" and "f(x)" in LaTex style.

{{{ continue from paused state }}}

Since we need LaTex style formatting, all we have to do is enclose the string

in between two $. Hence,

::

    xlabel("$x$")

    yalbel("$f(x)$")

does the job for us.

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

The plot is now almost complete. Except that we have still not seen how to 

name the points. For example the point (2, -1) is the local maxima. We would

like to name the point accordingly. We can do this by using

::

    annotate("local maxima", xy=(2, -1))

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

As you can see, the first argument to =annotate= command is the name we would

like to mark the point as and the argument after xy= is the point at which the

name should appear.

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%% 6 %% Make an annotation called "root" at the point (-4, 0)

        What happens to the first annotation ?

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

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we have looked at 

 * Modifying the attributes of plot by passing additional arguments

 * How to add title

 * How to incorporate LaTex style formatting

 * How to label x and y axes

 * How to add annotations

{{{ Show the "sponsored by FOSSEE" slide }}}

#[Nishanth]: Will add this line after all of us fix on one.

This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

Hope you have enjoyed and found it useful.

Thankyou

.. Author              : Nishanth

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