*Publication quality 2D plots can be produced by matplotlib, which is an open source object-oriented Python library. With this article, we begin a series that will take the reader through the nuances of 2D plotting with matplotlib.*

*matplotlib* is a Python library for creating 2D plots. It was originally created by John D. Hunter and is now maintained by a large team of developers. It integrates well with *IPython* – the component in the standard scientific Python toolset. *matplotlib* uses NumPy – a fundamental package for scientific computing with Python. The *matplotlib* code is conceptually divided into three parts — the pylab interface, the front-end and the back-end. The *pylab interface* is a set of functions which allow the user to create plots. The front-end (matplotlib API) is a set of classes for creating and managing figures, text, lines, plots, etc. Basically, this is an abstract interface. The back-end is a drawing device (renderer) that transforms the front-end representation to a hard copy or a display device.

**Installation**

Use the following commands to install *matplotlib*:

python –m pip install -U pip setuptools python –m pip install matplotlib

**Pyplot**

*matplotlib.pylot* is a collection of command style functions. Each function makes some change to a figure, like creating a figure, creating a plotting area in a figure, decorating the plot with labels, etc. Now, let us create a very simple plot for some given data, as shown below:

import matplotlib.pyplot as plt plt.plot([1,2,3,4]) plt.ylabel(‘Y values’) plt.show()If you provide a single list array to the

*plot()*command,

*matplotlib*assumes it is a sequence of Y values and internally generates the X value for you. The output is shown in Figure 1.

We do not need to worry about window creation and other basic event handling.

*matplotlib*provides some basic operations of the plot. The basic operations are:

*Reset original view, Back to previous view, Forward to next view, Pan axes with left mouse, Zoom with right, Zoom to rectangle, Configure subplots*and

*Save the figure*. If you click on the ‘Configure subplots’ button, another window with the following parameters will open:

*left, bottom, right, top, wspace,*and

*hspace*to adjust the plot (see Figure 2).

To plot X versus Y, we can use the commands shown below, as *plot()* takes an arbitrary number of arguments.

import matplotlib.pyplot as plt plt.plot([1, 2, 3, 4], [1, 4, 9, 16]) plt.xlabel(‘X values’) plt.ylabel(‘Y values’) plt.show()

The output of the code above is shown in Figure 3.

To control the axis, *matplotlib* has the *axis()* command; it takes a list of values (Xmin, Xmax, Ymin, Ymax) and also specifies the viewport of the axes.

To plot several lines with different styles, use the following commands:

import matplotlib.pyplot as plt import numpy as np x = np.arange(10) plt.plot(x, x, ‘g’) plt.plot(x, 2 * x, ‘r--’) plt.plot(x, 3 * x, ‘g^’) plt.plot(x, 4 * x, ‘bs’) plt.legend([‘y = x’, ‘y = 2x’, ‘y = 3x’, ‘y = 4x’], loc=’upper left’) plt.show()

**Controlling line properties**

We can set many attributes to a line. The Table 1 shows a list of available *Line2D* properties.

**Adding text into the plot**

The *text()* command can be used to add text in an arbitrary location. The* xlabel(), ylabel()* and *title()* are used to add text in the indicated locations. The code below creates a histogram and some text. The output is shown in Figure 5.

import numpy as np import matplotlib.pyplot as plt mu, sigma = 100, 15 x = mu + sigma * np.random.randn(10000) # the histogram of the data n, bins, patches = plt.hist(x, 50, normed=1, facecolor=’g’, alpha=0.75) plt.xlabel(‘Smarts’) plt.ylabel(‘Probability’) plt.title(‘Histogram of IQ’) plt.text(60, .025, r’$\mu=100,\ \sigma=15$’) plt.axis([40, 160, 0, 0.03]) plt.grid(True) plt.show()

This is only an introductory article on *matplotlib*. Next month, we will explore the topic in greater depth along with examples. The code is taken from *http://matplotlib.org* and readers are advised to look at the examples provided at *http://matplotlib.org/examples/index.html*.

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