1 Hello friends. Welcome to this spoken tutorial on Multiple plots.

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     3 {{{ Show the slide containing the title }}}

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     5 {{{ Show the slide containing the outline }}}

     6 

     7 In this tutorial, we will learn how to draw more than one plot, how to

     8 add legends to each plot to indicate what each plot represents. We

     9 will also learn how to switch between the plots and creating multiple

    10 plots with different regular axes which are also called as subplots.

    11 

    12 {{{ Shift to terminal and start ipython -pylab }}}

    13 

    14 To begin with let us start ipython with pylab, by typing::

    15 

    16   ipython -pylab

    17 

    18 on the terminal

    19 

    20 Let us first create set of points for our plot. For this we will use

    21 the command called linspace::

    22 

    23   x = linspace(0, 50, 10)

    24 

    25 linspace command creates 10 points in the interval between 0 and 50

    26 both inclusive. We assign these values to a variable called x.

    27 

    28 Now let us draw a plot simple sine plot using these points::

    29 

    30   plot(x, sin(x))

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    32 This should give us a nice sine plot.

    33 

    34 {{{ Switch to the plot window }}}

    35 

    36 Oh! wait! Is that a nice sine plot? Does a sine plot actually look

    37 like that? We know that a sine plot is a smooth curve is it not? What

    38 really caused this?

    39 

    40 {{{ pause for a while }}}

    41 

    42 A small investigation on linspace tells us that we chose too few

    43 points in a large interval between 0 and 50 for the curve to be

    44 smooth. So now let us use linspace again to get 500 points between 0

    45 and 100 and draw the sine plot

    46 

    47 {{{ Switch to ipython andtype }}} ::

    48 

    49   y = linspace(0, 50, 500)

    50   plot(y, sin(y))

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    52 {{{ Change to the plot window }}}

    53 

    54 Now we see what we remember as a sine plot. A smooth curve. If we

    55 carefully notice we also have two plots now one overlaid upon

    56 another. In pylab, by default all the plots are overlaid.

    57 

    58 We now know how to draw multiple plots but we would like to have more

    59 control over it. Like switch between them, perform some operations or

    60 labelling on them individually and so on. Let us see how to accomplish

    61 this. Before we move on, let us clear our screen.

    62 

    63 {{{ Switch to ipython }}}::

    64 

    65   clf()

    66 

    67 To accomplishing more control over individual plots we use the figure

    68 command::

    69 

    70   x = linspace(0, 50, 500)

    71   figure(1)

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

    73   figure(2)

    74   plot(x, cos(x), 'g')

    75 

    76 {{{ Switch to plot window }}}

    77 

    78 Now we have two plots, a sine plot and a cosine plot one overlaid upon

    79 the other.

    80 

    81 {{{ Have both plot window and ipython side by side }}}

    82 

    83 The figure command takes an integer as an argument which is the serial

    84 number of the plot. This selects the corresponding plot. All the plot

    85 commands we run after this are applied to the selected plot. In this

    86 example figure 1 is the sine plot and figure 2 is the cosine plot. We

    87 can, for example, save each plot separately

    88 

    89 {{{ Switch to ipython }}}::

    90 

    91   savefig('/home/user/cosine.png')

    92   figure(1)

    93   title('sin(y)')

    94   savefig('/home/user/sine.png')

    95 

    96 {{{ Have both plot window and ipython side by side }}}

    97 

    98 We also titled the our first plot as 'sin(y)' which we did not do for

    99 the second plot.

   100 

   101 Since we have two plots now overlaid upon each other we would like to

   102 have a way to indicate what each plot represents to distinguish

   103 between them. This is accomplished using legends. Equivalently, the

   104 legend command does this for us

   105 

   106 {{{ Switch to ipython }}}::

   107 

   108   legend(['sin(x)', 'cos(x)'])

   109 

   110 The legend command takes a single list of parameters where each

   111 parameter is the text indicating the plots in the order of their

   112 serial number.

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   114 {{{ Switch to plot window }}}

   115 

   116 Now we can see the legends being displayed for the respective sine and

   117 cosine plots on the plot area.

   118 

   119 At times we run into situations where we want to compare two plots and

   120 in such cases we want to draw both the plots in the same plotting

   121 area. The situation is such that the two plots have different regular

   122 axes which means we cannot draw overlaid plots. In such cases we can

   123 draw subplots.

   124 

   125 We use subplot command to accomplish this

   126 

   127 {{{ Switch to ipython }}}::

   128 

   129   subplot(2, 1, 1)

   130 

   131 subplot command takes three arguments, the first being the number of

   132 rows of subplots that must be created,

   133 

   134 {{{ Have both plot window and ipython side by side }}}

   135 

   136 in this case we have 2 so it spilts the plotting area horizontally for

   137 two subplots. The second argument specifies the number of coloumns of

   138 subplots that must be created. We passed 1 as the argument so the

   139 plotting area won't be split horizontally and the last argument

   140 specifies what subplot must be created now in the order of the serial

   141 number. In this case we passed 1 as the argument, so the first subplot

   142 that is top half is created. If we execute the subplot command as

   143 

   144 {{{ Switch to ipython }}}::

   145 

   146   subplot(2, 1, 2)

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   148 {{{ Switch to plot window }}}

   149 

   150 The lower subplot is created. Now we can draw plots in each of the

   151 subplot area using the plot command.

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   153 {{{ Switch to ipython }}}::

   154 

   155   x = linspace(0, 50, 500)

   156   plot(x, cos(x))

   157   subplot(2, 1, 1)

   158   y = linspace(0, 5, 100)

   159   plot(y, y ** 2)

   160 

   161 {{{ Have both plot window and ipython side by side }}}

   162 

   163 This created two plots one in each of the subplot area. The top

   164 subplot holds a parabola and the bottom subplot holds a cosine

   165 curve.

   166 

   167 As seen here we can use subplot command to switch between the subplot

   168 as well, but we have to use the same arguments as we used to create

   169 that subplot, otherwise the previous subplot at that place will be

   170 automatically erased. It is clear from the two subplots that both have

   171 different regular axes. For the cosine plot x-axis varies from 0 to

   172 100 and y-axis varies from 0 to 1 where as for the parabolic plot the

   173 x-axis varies from 0 to 10 and y-axis varies from 0 to 100

   174 

   175 {{{ Show summary slide }}}

   176 

   177 This brings us to the end of another session. In this tutorial session

   178 we learnt

   179 

   180  * How to draw multiple plots which are overlaid

   181  * the figure command

   182  * how to switch between the plots and perform some operations on each

   183    of them like saving the plots

   184  * the legend command and

   185  * creating and switching between subplots

   186 

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

   188 

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

   190 

   191 Hope you have enjoyed and found it useful.

   192 Thankyou

   193  

   194 .. Author              : Madhu

   195    Internal Reviewer 1 :         [potential reviewer: Puneeth]

   196    Internal Reviewer 2 :         [potential reviewer: Nishanth]

   197    External Reviewer   :

   198