Examples of MARX in useΒΆ

This section contains examples of marx in use from rather trivial use cases to complex and demanding analysis scripts. Going through these examples is the best way to discover the power of marx. They also provide a great starting point for developing your own analysis.

All examples assume that you are working in a directory where you have write permission and enough disk space for the simulation. It is also assumed that the marx executables are on the search path and that the marx parameter files marx.par, marxasp.par, and marxpileup.par are located in the current directory or in the path of your PFILES environment variable. If you installed marx as described in Downloading and Installing Marx, the latter requirement may be accomplished by running:

unix% marx --help
  .
  .
marx parameter files may be found in:
 /opt/marx5.5/share/marx/pfiles/

Simply copy the files from the indicated directory to the current one:

unix% cp /opt/marx5.5/share/marx/pfiles/*.par .

In most examples, marx is used together with a spectral analysis program to write the input spectrum or to analyze the results. The most common programs are Xspec, Sherpa, and ISIS. Our examples use Sherpa, because it is typically installed when you install CIAO. It should be easy to adapt the examples for other spectral analysis systems as well.

We use Python as a scripting language and the Python interface to CIAO to call CIAO tools. Even if you are not familiar with Python, it should not be difficult to convert the examples to shell scripts. For example:

rt.dmcopy(f"marx_saotrace.fits[@{evt2file}[GTI4]]", "marx_saotrace-filtered.fits", clobber=True)

translates to a command line of:

unix% dmcopy "marx_saotrace.fits[@${evt2file}[GTI4]]" marx_saotrace-filtered.fits clobber=yes

marx itself currently does not have a nice Python interface, so to call marx we simply pass a string directly from Python to the shell, such as:

import subprocess
out = subprocess.call('marx SourceType="point" OutputDir="result"', shell=True)

which is the equivalent of the shell command:

unix% marx SourceType="point" OutputDir="result"

If we run marx multiple times in one example, we can use Python to parameterize that:

for i in range(5):
    out = subprocess.call(f'marx MinEnergy={i} MaxEnergy={i+1} OutputDir="result_{i}"', shell=True)

Still, it should not be difficult to convert these examples to shell scripts so that they can be pasted directly on the command line.

We present the following examples:

Further examples of marx use can be found on the CIAO thread pages: