Dear All,
How to find virial radius from enzo output. From the following page 
http://yt-project.org/docs/2.6/reference/api/generated/yt.analysis_modules.halo_finding.halo_objects.FOFHalo.virial_radius.html?highlight=virial%20radius#yt.analysis_modules.halo_finding.halo_objects.FOFHalo.virial_radius

I came to know that there is a function called virial_radius(). But how to use it?
In the provided example 
>>> vr = halos[0].virial_radius()
what is ' halos[0] ' ?

Thank You
 

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Reju Sam John