[yt-users] Defining a new field, including IF statement

[Yusuke Fujimoto]

Dear yt-users,

I am trying to define a new field, SFR_Density, which includes if
statements.
That is defined by,
f_sf * rho / t_ff  if rho > rho_threshold
0                      if rho < rho_threshold
(f_sf is star formation efficiency, rho is gas density, and t_ff is free
fall time)

Here is my definition I tried.

def _SFR_Density(field, data):

   f_sf = 0.01

   rho_thresh = 57.5 * Mu * hydrogen_mass

   if data["density"] > rho_thresh:

      return f_sf * data["density"] / (3*pi/32/Grav/data["density"])**(0.5)

   else:

      return 0.0 * f_sf * data["density"] / (3*pi/32/Grav/data["density"
])**(0.5)

add_field("SFR_Density", function=_SFR_Density)

But it fails with an error message of "ValueError: The truth value of an
array with more than one element is ambiguous. Use a.any() or a.all()"
I am sure this is because data["density"] is a list, so I need to specify
the exact index number of elements at the if statement. I have tried many
tests, but now I am in stuck.

Any help would be very appreciated.

Thanks,
Yusuke
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