# Usage of Matplotlib in Python

Python is a great general-purpose programming language on its own, but with the help of a few popular libraries (numpy, scipy, matplotlib) it becomes a powerful environment for scientific computing.

We expect that many of you will have some experience with Python and numpy; for the rest of you, this section will serve as a quick crash course both on the Python programming language and on the use of Python for scientific computing.

Some of you may have previous knowledge in Matlab, in which case we also recommend the numpy for Matlab users page.

### Matplotlib

Matplotlib is a plotting library. In this section give a brief introduction to the `matplotlib.pyplot` module, which provides a plotting system similar to that of MATLAB.

### Plotting

The most important function in matplotlib is `plot`, which allows you to plot 2D data. Here is a simple example:

``````import numpy as np
import matplotlib.pyplot as plt

# Compute the x and y coordinates for points on a sine curve
x = np.arange(0, 3 * np.pi, 0.1)
y = np.sin(x)

# Plot the points using matplotlib
plt.plot(x, y)
plt.show()  # You must call plt.show() to make graphics appear.
``````

Running this code produces the following plot: With just a little bit of extra work we can easily plot multiple lines at once, and add a title, legend, and axis labels:

``````import numpy as np
import matplotlib.pyplot as plt

# Compute the x and y coordinates for points on sine and cosine curves
x = np.arange(0, 3 * np.pi, 0.1)
y_sin = np.sin(x)
y_cos = np.cos(x)

# Plot the points using matplotlib
plt.plot(x, y_sin)
plt.plot(x, y_cos)
plt.xlabel(\'x axis label\')
plt.ylabel(\'y axis label\')
plt.title(\'Sine and Cosine\')
plt.legend([\'Sine\', \'Cosine\'])
plt.show()
`````` You can read much more about the `plot` function in the documentation.

### Subplots

You can plot different things in the same figure using the `subplot` function. Here is an example:

``````import numpy as np
import matplotlib.pyplot as plt

# Compute the x and y coordinates for points on sine and cosine curves
x = np.arange(0, 3 * np.pi, 0.1)
y_sin = np.sin(x)
y_cos = np.cos(x)

# Set up a subplot grid that has height 2 and width 1,
# and set the first such subplot as active.
plt.subplot(2, 1, 1)

# Make the first plot
plt.plot(x, y_sin)
plt.title(\'Sine\')

# Set the second subplot as active, and make the second plot.
plt.subplot(2, 1, 2)
plt.plot(x, y_cos)
plt.title(\'Cosine\')

# Show the figure.
plt.show()
`````` You can read much more about the `subplot` function in the documentation.

Cheers!!!

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