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+++ b/embellishing_a_plot/script.rst Thu Oct 07 14:25:44 2010 +0530
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+.. Objectives
+.. ----------
+
+.. A - Students and teachers from Science and engineering backgrounds
+ B -
+ C -
+ D -
+
+.. Prerequisites
+.. -------------
+
+.. 1. Using the ``plot`` command interactively
+
+.. Author : Nishanth Amuluru
+ Internal Reviewer :
+ External Reviewer :
+ Checklist OK? : <put date stamp here, if OK> [2010-10-05]
+
+Script
+------
+
+Hello friends and welcome to the tutorial on Embellishing Plots.
+
+{{{ Show the slide containing title }}}
+
+{{{ Show the slide containing the outline }}}
+
+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 and setting the limits of axes.
+
+Let us start ipython with pylab loaded, by typing on the terminal
+
+{{{ shift to terminal and type ipython -pylab }}}
+
+::
+
+ ipython -pylab
+
+.. #[madhu: I feel the instructions should precede the actual action,
+
+since while recording we need to know before hand what we need to do]
+
+We shall first make a simple plot and start decorating it.
+
+.. #[madhu: start decorating it should be fine, with is not necessary]
+
+::
+
+ x = linspace(-2, 4, 20)
+ plot(x, sin(x))
+
+.. #[madhu: Standard is to choose between -50 to 50 or 0 to 50 with 100
+ points right?]
+
+As we can see, the default colour and the default thickness of the
+line is as decided by pylab. Wouldn't be nice if we could control
+these parameters in the plot? This is possible by passing additional
+arguments to the plot command.
+
+.. #[[Anoop: I think it will be good to rephrase the sentence]]
+.. #[madhu: Why "you" here? Shouldn't this be "we" as decided? Also I
+ added "the default" check the diff]
+
+The additional argument that we shall be passing in here now is the
+colour argument. We shall first clear the figure and plot the same in
+red colour. Hence
+
+.. #[Madhu: Note the diff for changes]
+ ::
+
+ clf()
+ plot(x, sin(x), 'r')
+
+As we can see we have the same plot but now in red colour.
+
+.. #[Madhu: diff again]
+
+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, to be more precise plot with line
+thickness 2.
+
+.. #[[Anoop: I guess it will be good if you say that it affects the
+ same plot, as you have not cleared the figure]]
+.. #[Madhu: To Anoop, not necessary I feel since they can see it?]
+
+{{{ Show the plot and compare the sine and cos plots }}}
+
+{{{ Pause here and try out the following exercises }}}
+
+.. #[[Anoop: is the above a context switch for the person who does the
+ recording, other wise if it an instruction to the person viewing
+ the video, then I guess the three braces can be removed.]]
+
+%% 1 %% Plot sin(x) in blue colour and with linewidth as 3
+
+{{{ continue from paused state }}}
+
+A combination of colour and linewidth would do the job for us. Hence
+::
+
+ clf()
+ plot(x, sin(x), 'b', linewidth=3)
+
+.. #[[Anoop: add clf()]]
+
+produces the required plot
+
+.. #[Nishanth]: I could not think of a SIMPLE recipe approach for
+ introducing linestyle. Hence the naive approach.
+
+.. #[[Anoop: I guess the recipe is fine, but would be better if you
+ add the problem statement rather than just saying "let's do a simple
+ plot"]]
+
+.. #[Madhu: It is good enough.]
+
+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 }}}
+
+{{{ Show the options available for line style and colors }}}
+
+.. #[Madhu: The script needs to tell what needs to be shown or
+ explained.]
+
+{{{ Pause here and try out the following exercises }}}
+
+.. #[[Anoop: same question as above, should it be read out?]]
+
+%% 2 %% Plot the sine curve with green filled circles.
+
+{{{ continue from paused state }}}
+
+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 %% Plot the curve of x vs tan(x) in red dashed line and linewidth 3
+
+{{{ continue from paused state }}}
+
+.. #[Madhu: I did not understand the question]
+
+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 not have any description describing the plot.
+
+.. #[Madhu: Added "not". See the diff]
+
+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 an argument and sets
+the title accordingly.
+
+.. #[Madhu: See the diff]
+
+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 in 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
+
+.. #[[Anoop: I guess you can go ahead with the LaTex thing, it's
+ cool!]]
+.. #[Madhu: Instead of saying LaTeX style you can say Typeset math
+ since that is how it is called as. I am not sure as well. It
+ doesn't really solve the purpose]
+
+{{{ 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
+
+{{{ continue from the paused state }}}
+
+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 an argument,
+similar to the ``title`` command and sets it as the label to x-axis.
+
+.. #[See the diff]
+
+Similarly,
+::
+
+ ylabel("f(x)")
+
+sets the name of the y-axis as "f(x)"
+
+{{{ Show the plot window and point to ylabel and switch back to the 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 second argument is the co-ordinates of the
+point at which the name should appear. It is a sequence containing two numbers.
+The first is x co-ordinate and second is y co-ordinate.
+
+.. #[[Anoop: I think we should tell explicitely that xy takes a
+ sequence or a tuple]]
+.. #[Madhu: Agreed to what anoop says and also that xy= is the point
+ part should be rephrased I think.]
+
+{{{ Pause here and try out the following exercises }}}
+
+%% 6 %% Make an annotation called "root" at the point (-4, 0)
+ What happens to the first annotation ?
+
+{{{ continue from paused state }}}
+
+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 is possible using the
+button on the plot window.
+
+we shall look at how to get and set them from the script.
+::
+
+ xlim()
+ ylim()
+
+We see that ``xlim`` function returns the current x axis limits and ylim
+function returns the current y-axis limits.
+
+Let us look at how to set the limits.
+::
+
+ xlim(-4, 5)
+
+We see the limits of x-axis are now set to -4 and 5.
+Similarly
+::
+
+ ylim(-15, 2)
+
+sets the limits of y-axis appropriately.
+
+{{{ Pause here and try out the following exercises }}}
+
+%% 7 %% Set the limits of axes such that the area of interest is the rectangle
+ (-1, -15) and (3, 0)
+
+{{{ continue from paused state }}}
+
+As we can see, the lower upper limits of x-axis in the question are -1 and 3.
+The limits of y-axis are -15 and 0.
+
+::
+
+ xlim(-1, 3)
+ ylim(-15, 0)
+
+Gives us the required rectangle.
+
+{{{ Show summary slide }}}
+
+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
+ * How to set the limits of axes
+
+{{{ 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
+
+