Matplotlib

The python distribution deployed on instruments includes a powerful plotting library called matplotlib.

Matplotlib is a highly customizable, general purpose plotting library capable of producing a wide variety of plot types. There are lots of tutorials and examples online, such as:

• Matplotlib tutorials
• Matplotlib examples
• matplotlib.pyplot command reference

Contents

• Quick-start
  • To import pyplot
  • Useful pyplot commands
  • Example: Plot and show a trivial graph
  • Example: Plot a constantly updating sin wave
• Plotting Spectra
• Using matplotlib within the IBEX GUI

Quick-start

To import pyplot

The most user-friendly interface to matplotlib is called pyplot. You can import pyplot using the following command:

import matplotlib.pyplot as pyplot

Useful pyplot commands:

• pyplot.plot(): Populate a plot with some data.
• pyplot.clf(): Clear the current figure, e.g. discard old data from the plot.
• pyplot.show(): Shows the matplotlib plotting window.
• pyplot.draw(): Draws updates to a plot that is already open.
• pyplot.close('all'): Closes all plots and removes all data.
• pyplot.close(n): Close a specific figure.
• pyplot.figure(): Creates a new figure.
• pyplot.figure(n): Creates or switches to figure n.

Example: plot and show a trivial graph

import matplotlib.pyplot as pyplot
pyplot.plot(range(10))
pyplot.show()

Example: plot a constantly-updating sin wave

import matplotlib.pyplot as pyplot
from math import sin
from time import time, sleep

# Create a new figure.
pyplot.figure()

# Show plot - only need to do this once,! (this will display the blank figure)
pyplot.show()

while True:
    # Clear the old data from the figure - we want to replace it completely.
    pyplot.clf()  
    # Plot our new data onto the figure.
    pyplot.plot([sin(x/1000.0 + time()) for x in range(10000)])
    # Draw the new data to the screen.
    pyplot.draw()
    # Short sleep to avoid going into a tight loop and using 100% processor.
    sleep(0.5)

Plotting spectra

The genie_python library includes commands to plot the neutron spectra on an instrument quickly.

Plot a single spectrum:

g.plot_spectrum(1)

Plot several spectra on one graph:

graph = g.plot_spectrum(1)
graph.add_spectrum(2)
graph.add_spectrum(3, period=2)

Plot several spectra on different graphs:

g.plot_spectrum(1)
g.plot_spectrum(2)

For greater control over the exact presentation or contents of the spectra plots, the raw spectrum data can be acquired using:

g.get_spectrum(spectrum=1)

Using matplotlib within the IBEX GUI

The IBEX user interface includes a python scripting window. When plotting graphs within IBEX, matplotlib is configured to display the plot within the IBEX gui.

In the IBEX user interface, matplotlib is non-blocking - that is, a script will continue once a plot has been drawn without the plot needing to be closed.

Note: this is new functionality as of July 2018. If you prefer matplotlib windows to spawn separately from the main IBEX window, you can type the matplotlib command:

matplotlib.use('Qt4Agg')

This needs to be typed before any matplotlib functionality is used for it to take effect.

Troubleshooting

Only 3 plots can be opened at once

By default, only 3 plots can be opened at a time. If this limit is exceeded, the oldest plot will be automatically removed.