Matplotlib Examples

matplotlib is used to plot data. It is a very powerful library that is interfaced to TRIQS.

Goal of this tutorial

This is an illustration of an ipython notebook. It will plot the functions

\[f(x) = e^x \sin(5x)\]

and

\[f(x) = e^x \cos(5x)\]

Afterwards we’ll see how to create and modify plots.

Inline plots

In order to have access to numpy and matplotlib commands and to plot directly in the notebook, run:

import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline
# change scale of all figures to make them bigger
import matplotlib as mpl
mpl.rcParams['figure.dpi']=100

# The plot command takes the x coordinates as first argument
# then the y coordinates. The third argument controls the
# way points look on the plot

xr = np.arange(0,3,0.1)
yr1 = np.exp(xr) * np.sin(5*xr)
yr2 = np.exp(xr) * np.cos(5*xr)

plt.plot(xr, yr1, '-r', lw=3, label = 'red line')
plt.plot(xr, yr2, 'xb', label = 'blue line')
plt.legend()

<matplotlib.legend.Legend at 0x10d970050>

Making the plot prettier

We start off with the simplest example of a single plot. Note how you can change the line style, its width, the color and the symbols. The labels of the axis and their range is easily controlled.

xr = np.arange(0,1,0.01)
yr = np.sin(xr)
plt.plot(xr,yr,'--b',lw=4)
plt.plot([-0.5,1.5],[0.0,0.4],'-g^',label='a line')
plt.legend()
plt.xlabel('time $t$')
plt.ylabel('$\int \,dt\, \cos(t)$')
plt.axis([-1,2,-0.2,1.1])

(-1.0, 2.0, -0.2, 1.1)

Subplots

When you want to create subplots, you first have to create a figure. Then with the command

subplot(l,m,i)

you can create an \(l \times m\) array of plots and select the \(i\)-th subplot.

xr = np.arange(0,10,0.01)
plt.figure(1)
plt.subplot(2,1,1)
plt.plot(xr,np.sin(xr),'b')
plt.title("subplot 1")
plt.ylabel('sin')
plt.subplot(2,1,2)
plt.plot(xr,np.cos(xr),'r')
plt.title("subplot 2")
plt.ylabel('cos')
plt.xlabel(r'$\omega$',)
plt.figure(2)
plt.plot(xr,np.exp(-0.1*xr**2),label='some function here')
plt.legend()
plt.title("figure 2")

Text(0.5, 1.0, 'figure 2')

Histograms and text

The example below shows how to create a histogram and how to add text in the plot. Note how \(\alpha = 0.3\) is used to control transparency.

mu, sigma = 100, 15
x = mu + sigma * np.random.randn(10000)
xr = np.arange(50,150,0.1)

plt.hist(x, 50, density=1, facecolor='r', alpha=0.3)
plt.plot(xr,0.028*np.exp(-0.0025*(xr-100)**2),'b',lw=3)

plt.xlabel('Smarts')
plt.ylabel('Probability')
plt.title('Histogram')
plt.text(45, .025, r'$\mu=100,\ \sigma=15$',fontsize=20)
plt.axis([40, 160, 0, 0.03])
plt.grid(True)

Python-like approach to matplotlib

Above, we have used a matlab-like commands to control the plot creation. Behind the curtains matplotlib still works with python objects, so that a figure is a python object. Adding a plot in the figure is then done with the

add_axes

command. This creates an “axes” object (a plot). Calling the methods

set_title
set_xlabel, ...

you can act on the different parts of the plot, etc. This approach is very powerful and allows to quite easily put an inset in your plot.

xr = np.arange(0,3,0.2)
yr = np.tanh(xr)

fig = plt.figure(1)
ax = fig.add_axes([0., 0.8, 1.5, 0.9])
ax.set_title("My axes",fontsize=20)
ax.set_xlabel(r'$x$',fontsize=20)
ax.set_ylabel(r'$\tanh(x)$',fontsize=20)
ax.plot(xr,yr,'o')
subax = fig.add_axes([0.45,0.85,1.,0.5])
subax.plot(xr,np.sin(xr),'r',label='sinus')
plt.legend()

<matplotlib.legend.Legend at 0x10dd56810>

More examples

Here are some additional examples. They summarize what is described above.

xr = np.arange(0,3,.1)
yr1 = np.exp(xr)*(np.sin(5*xr))
yr2 = np.exp(xr)*(np.cos(5*xr))
plt.figure(1)
plt.plot(xr,yr1,'-r',lw=3, label='a first curve')
plt.plot(xr,yr2,'--b',lw=3, label='$e^{x} \cos(5 x)$')
plt.legend()
plt.xlabel('time $t$')
plt.ylabel('$\int \, \cos(t) $')

plt.figure(2)
plt.plot(xr,yr1*3.,'-.b^',lw=1, label='a second curve')
plt.legend()
plt.xlabel('time $t$')
plt.ylabel('$\int \, \cos(t) $')


plt.figure(3)
plt.subplot(211)
plt.plot(xr,yr1,'-r',lw=3, label='a first curve')
plt.legend()
plt.ylabel('$\int \, \cos(t) $')
plt.subplot(212)
plt.plot(xr,yr2,'--b',lw=3, label='$e^{x} \cos(5 x)$')
plt.legend()
plt.xlabel('time $t$')
plt.ylabel('$\int \, \cos(t) $')


plt.figure(4)

plt.subplot(121)
plt.title('My title')
plt.plot(xr,yr1,'-r',lw=3, label='a first curve')
plt.legend()
plt.ylabel('$\int \, \cos(t) $')
plt.xlabel('time $t$')
plt.subplot(122)
plt.grid(True)
plt.plot(xr,yr2,'--b',lw=3, label='$e^{x} \cos(5 x)$')
plt.legend()
plt.xlabel('time $t$')

plt.figure(5)

a = np.loadtxt("sample.dat")
plt.plot(a[:,0],a[:,1],'-o')

[<matplotlib.lines.Line2D at 0x10db27a90>]