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

[Britton Smith]

Sorry, even that's not right.  Clearly, it's too early for me!

field_data[np.invert(threshold)] = 0

There may be other typos, but in general, this should work.

Britton

On Thu, Nov 2, 2017 at 6:01 AM, Britton Smith <brittonsmith at gmail.com>
wrote:

> Hi again,
>
> There's a small typo.  This line:
> field_data[np.invert(threshold] = 0
> is missing the closing bracket:
> field_data[np.invert(threshold]] = 0
>
> On Thu, Nov 2, 2017 at 6:00 AM, Britton Smith <brittonsmith at gmail.com>
> wrote:
>
>> Hi Yusuke,
>>
>> This error comes from the fact that your field function is being
>> evaluated for an array of elements all at once.  You will likely have
>> portions of the array that satisfy both criteria.  You'll need to first
>> define a field array and then set the values for the portions above the
>> density threshold and then below.  I recommend doing something like the
>> following:
>>
>> def _SFR_Density(field, data):
>>    f_sf = 0.01
>>    rho_thresh = 57.5 * Mu * hydrogen_mass
>>    # make field array
>>    field_data = data["density"].copy()
>>    # density threshold
>>    threshold = data["density"] > rho_thresh
>>    # set values above threshold
>>    field_data[threshold] *= f_sf * / (3*pi/32/Grav/data["density"])
>> **(0.5)
>>    # set values below
>>    field_data[np.invert(threshold] = 0
>>    return field_data
>>
>> The threshold array is a boolean array that can be used to access all the
>> values satisfying your criteria all at once.  Then, the np.invert gives you
>> all the values not satisfying it.  Hope that helps!
>>
>> Britton
>>
>> On Wed, Nov 1, 2017 at 10:46 PM, Yusuke Fujimoto <
>> yusuke.fujimoto.jp at gmail.com> wrote:
>>
>>> 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
>>>
>>> _______________________________________________
>>> yt-users mailing list
>>> yt-users at lists.spacepope.org
>>> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>>>
>>>
>>
>
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