1 .. Objectives

     2 .. ----------

     3 

     4 .. A - Students and teachers from Science and engineering backgrounds

     5    B - 

     6    C - 

     7    D - 

     8 

     9 .. Prerequisites

    10 .. -------------

    11 

    12 ..   1. Using the ``plot`` command interactively

    13      

    14 .. Author              : Nishanth Amuluru

    15    Internal Reviewer   : 

    16    External Reviewer   :

    17    Checklist OK?       : <put date stamp here, if OK> [2010-10-05]

    18 

    19 Script

    20 ------

    21 

    22 Hello friends and welcome to the tutorial on Embellishing Plots.

    23 

    24 {{{ Show the slide containing title }}}

    25 

    26 {{{ Show the slide containing the outline }}}

    27 

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

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

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

    31 annotations to the plot and setting the limits of axes.

    32 

    33 Let us start ipython with pylab loaded, by typing on the terminal

    34 

    35 {{{ shift to terminal and type ipython -pylab }}}

    36 

    37 ::

    38 

    39     ipython -pylab

    40 

    41 .. #[madhu: I feel the instructions should precede the actual action,

    42 

    43 since while recording we need to know before hand what we need to do]

    44 

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

    46 

    47 .. #[madhu: start decorating it should be fine, with is not necessary]

    48 

    49 ::

    50 

    51     x = linspace(-2, 4, 20)

    52     plot(x, sin(x))

    53 

    54 .. #[madhu: Standard is to choose between -50 to 50 or 0 to 50 with 100

    55      points right?]

    56 

    57 As we can see, the default colour and the default thickness of the

    58 line is as decided by pylab. Wouldn't be nice if we could control

    59 these parameters in the plot? This is possible by passing additional

    60 arguments to the plot command.

    61 

    62 .. #[[Anoop: I think it will be good to rephrase the sentence]]

    63 .. #[madhu: Why "you" here? Shouldn't this be "we" as decided? Also I

    64      added "the default" check the diff]

    65 

    66 The additional argument that we shall be passing in here now is the

    67 colour argument. We shall first clear the figure and plot the same in

    68 red colour. Hence

    69 

    70 .. #[Madhu: Note the diff for changes]

    71  ::

    72 

    73     clf()

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

    75 

    76 As we can see we have the same plot but now in red colour.

    77 

    78 .. #[Madhu: diff again]

    79 

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

    81 command. Hence

    82 ::

    83 

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

    85 

    86 produces a plot with a thicker line, to be more precise plot with line

    87 thickness 2.

    88 

    89 .. #[[Anoop: I guess it will be good if you say that it affects the

    90    same plot, as you have not cleared the figure]]

    91 .. #[Madhu: To Anoop, not necessary I feel since they can see it?]

    92 

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

    94 

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

    96 

    97 .. #[[Anoop: is the above a context switch for the person who does the

    98    recording, other wise if it an instruction to the person viewing

    99    the video, then I guess the three braces can be removed.]]

   100 

   101 %% 1 %% Plot sin(x) in blue colour and with linewidth as 3

   102 

   103 {{{ continue from paused state }}}

   104 

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

   106 ::

   107 

   108     clf()

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

   110 

   111 .. #[[Anoop: add clf()]]

   112 

   113 produces the required plot

   114 

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

   116              introducing linestyle. Hence the naive approach.

   117 

   118 .. #[[Anoop: I guess the recipe is fine, but would be better if you

   119    add the problem statement rather than just saying "let's do a simple

   120    plot"]]

   121 

   122 .. #[Madhu: It is good enough.]

   123 

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

   125 all we want is just a bunch of points not joined. This is possible by

   126 passing the linestyle argument along with or instead of the colour

   127 argument. Hence ::

   128 

   129     clf()

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

   131 

   132 produces a plot with only points.

   133 

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

   135 ::

   136 

   137     clf()

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

   139 

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

   141 ::

   142 

   143     plot?

   144 

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

   146 

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

   148 

   149 .. #[Madhu: The script needs to tell what needs to be shown or

   150      explained.]

   151 

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

   153 

   154 .. #[[Anoop: same question as above, should it be read out?]]

   155 

   156 %% 2 %% Plot the sine curve with green filled circles.

   157 

   158 {{{ continue from paused state }}}

   159 

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

   161 Hence

   162 ::

   163 

   164     clf()

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

   166 

   167 produces the required plot.

   168 

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

   170 

   171 %% 3 %% Plot the curve of x vs tan(x) in red dashed line and linewidth 3

   172 

   173 {{{ continue from paused state }}}

   174 

   175 .. #[Madhu: I did not understand the question]

   176 

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

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

   179 

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

   181 ::

   182 

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

   184 

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

   186 

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

   188 the figure does not have any description describing the plot.

   189 

   190 .. #[Madhu: Added "not". See the diff]

   191 

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

   193 ::

   194 

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

   196 

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

   198 

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

   200 ``title`` command as you can see, takes a string as an argument and sets

   201 the title accordingly.

   202 

   203 .. #[Madhu: See the diff]

   204 

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

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

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

   208 

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

   210 string that should be in LaTex style.

   211 

   212 for instance, we can use

   213 ::

   214 

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

   216 

   217 and we get the polynomial formatted properly.

   218 

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

   220              string in LaTex style is not good

   221 

   222 .. #[[Anoop: I guess you can go ahead with the LaTex thing, it's

   223      cool!]]

   224 .. #[Madhu: Instead of saying LaTeX style you can say Typeset math

   225      since that is how it is called as. I am not sure as well. It

   226      doesn't really solve the purpose]

   227 

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

   229 

   230 %% 4 %% Change the title of the figure such that the whole title is formatted

   231         in LaTex style

   232 

   233 {{{ continue from the paused state }}}

   234 

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

   236 ::

   237 

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

   239 

   240 gives a title that looks neatly formatted.

   241 

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

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

   244 

   245     xlabel("x")

   246 

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

   248 

   249 As you can see, ``xlabel`` command takes a string as an argument,

   250 similar to the ``title`` command and sets it as the label to x-axis.

   251 

   252 .. #[See the diff]

   253 

   254 Similarly,

   255 ::

   256 

   257     ylabel("f(x)")

   258 

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

   260 

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

   262 

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

   264 

   265 %% 5 %% Set the x and y labels as "x" and "f(x)" in LaTex style.

   266 

   267 {{{ continue from paused state }}}

   268 

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

   270 in between two $. Hence,

   271 ::

   272 

   273     xlabel("$x$")

   274     yalbel("$f(x)$")

   275 

   276 does the job for us.

   277 

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

   279 

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

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

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

   283 ::

   284 

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

   286 

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

   288 

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

   290 like to mark the point as and the second argument is the co-ordinates of the

   291 point at which the name should appear. It is a sequence containing two numbers.

   292 The first is x co-ordinate and second is y co-ordinate.

   293 

   294 .. #[[Anoop: I think we should tell explicitely that xy takes a

   295    sequence or a tuple]]

   296 .. #[Madhu: Agreed to what anoop says and also that xy= is the point

   297      part should be rephrased I think.]

   298 

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

   300 

   301 %% 6 %% Make an annotation called "root" at the point (-4, 0)

   302         What happens to the first annotation ?

   303 

   304 {{{ continue from paused state }}}

   305 

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

   307 

   308 Now we have everything we need to decorate a plot. but the plot would be

   309 incomplete if we can not set the limits of axes. This is possible using the

   310 button on the plot window.

   311 

   312 we shall look at how to get and set them from the script.

   313 ::

   314 

   315     xlim()

   316     ylim()

   317 

   318 We see that ``xlim`` function returns the current x axis limits and ylim

   319 function returns the current y-axis limits.

   320 

   321 Let us look at how to set the limits.

   322 ::

   323 

   324     xlim(-4, 5)

   325 

   326 We see the limits of x-axis are now set to -4 and 5.

   327 Similarly

   328 ::

   329 

   330     ylim(-15, 2)

   331 

   332 sets the limits of y-axis appropriately.

   333 

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

   335 

   336 %% 7 %% Set the limits of axes such that the area of interest is the rectangle

   337         (-1, -15) and (3, 0)

   338 

   339 {{{ continue from paused state }}}

   340 

   341 As we can see, the lower upper limits of x-axis in the question are -1 and 3.

   342 The limits of y-axis are -15 and 0.

   343 

   344 ::

   345 

   346     xlim(-1, 3)

   347     ylim(-15, 0)

   348 

   349 Gives us the required rectangle.

   350 

   351 {{{ Show summary slide }}}

   352 

   353 we have looked at 

   354 

   355  * Modifying the attributes of plot by passing additional arguments

   356  * How to add title

   357  * How to incorporate LaTex style formatting

   358  * How to label x and y axes

   359  * How to add annotations

   360  * How to set the limits of axes

   361 

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

   363 

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

   365 

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

   367 

   368 Hope you have enjoyed and found it useful.

   369 Thankyou

   370 

   371