Difference between revisions of "Python-3.4.3/C2/Embellishing-a-plot/English"

Objectives

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

System Requirements

• Ubuntu Linux 14.04 operating system
• Python 3.4.3
• IPython 5.1.0

Pre-requisites

• run basic Python commands on the ipython console
• and use the Plots interactively.

If not, see the pre-requisite Python tutorials on this website.

ipython3 and press Enter.

Open the terminal.

Type ipython3 and press Enter.

%pylab and press Enter.

Type percentage pylab and press Enter.

x = linspace(-2, 4, 20) and press Enter.

Type x = linspace inside the brackets minus 2 comma 4 comma 20 and press Enter.

The default colour and thickness of the line is as decided by pylab.

We can pass additional arguments to the plot command to do this.

clf() and press Enter.

plot(x, sin(x), 'r') and press Enter.

So we will type plot inside the brackets x comma sin(x) comma inside inverted commas r and press Enter.

Here, the argument 'r' is for red color.

Do not close the plot window just minimize it.

plot(x,cos(x),linewidth=2) and press Enter.

So, type plot inside the brackets x comma cos(x) comma linewidth equals to 2 and press Enter.

compare the sine and cosine plots

• press the Enter the key to execute every command
• that we type on the Ipython console.

clf()

You will again see a blank plot window.

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

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

clf()

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

plot?

Run through the information and show the options available

Show the options available for line style and colors

Type plot question mark and press Enter

Exercise 1

Plot the curve of x verses cos(x) in red dash line and linewidth 3.

clf()

plot(x, cos(x), 'r--',linewidth=3)

We use a combination of linewidth argument and linestyle.

Let us look at modifying the plot further.

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

Now type plot inside the brackets x comma minus x multiplied by x plus 4 multiplied by x minus 5 comma inside inverted commas r comma linewidth equals to 2

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

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

So type title inside the brackets inside inverted commas Parabolic function minus x square plus 4x minus 5

Highlight the title command

But it is not formatted and does not look clean.

Let us write the title in LaTeX format for a neater look.

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

Type title inside the brackets r inside inverted commas Parabolic function dollar minus x square plus 4x minus 5 dollar

Here ' r ' means that the string is to be treated as a raw string.

It will ignore all escape codes.

Point at the polynomial

xlabel(r"$x$")

ylabel(r"$y$")

So we will label x and y axes in LaTeX style.

Type xlabel inside the brackets r inside inverted commas dollar x dollar and ylabel inside brackets r inside inverted commas dollar y dollar

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

Now we will name the points considering point(2 comma minus 1) as local maxima.

To name a point, we use the function annotate.

Type annotate inside the brackets inside inverted commas local maxima comma xy equals to inside brackets 2 comma minus 1

Show the annotation that has appeared on the plot

Point at the annotate command while explaining

The second argument represents the coordinates of the point.

It is a tuple containing two numbers. The first is x coordinate and second is y coordinate.

xlim()

ylim()

xlim function returns the current x axis limits.

Then type ylim brackets

ylim function returns the current y-axis limits.

xlim(-4, 5)

ylim(-15, 2)

Similarly, set the limits of y-axis in a similar manner.

Type ylim inside the brackets minus 15 comma 2.

Exercise 2

Make an annotation called "root" at the point (minus 4 comma 0).

What happens to the first annotation?

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

Type annotate inside the brackets inside inverted commas root comma xy equals to inside brackets minus 4 comma 0

Every annotate command makes a new annotation on the figure.

Summary slide

1. Modify the attributes of a plot like color, line width, line style by passing additional arguments.
2. Add title to a plot using 'title command.
3. Incorporate LaTeX style formatting by adding a $ sign before and after the string.
4. Label x and y axes using xlabel() and ylabel() commands.
5. Add annotations to a plot using annotate() command.
6. Get and set the limits of axes using xlim() and ylim() commands.

Evaluation

1. Draw a plot of cosine graph between minus 2pi to 2pi with line thickness 4.
2. Read the documentation and find out, is there a way to modify the alignment of text in the command ylabel.

Solutions

1. In order to plot a cosine graph between the points minus 2pi and 2pi with line thickness 4,we use the linspace and plot command as,

x equals to linspace inside the brackets minus 2pi comma 2pi.

plot (x comma cos(x) comma linewidth equals to 4)

The answer to the second question is:

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

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Acknowledgement

Thank You