[yt-users] How to use if, elif, else statements in creating a derived field

[Kacper Kowalik]

On 10/21/2013 12:31 PM, Reju Sam John wrote:
> Dear Kacper,
>  This is my backtrace....
> 
> Traceback (most recent call last):
>   File "cosmic_ray_fra.py", line 50, in <module>
>     p = pc.add_slice("MyField", 2)
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/visualization/plot_collection.py",
> line 430, in add_slice
>     center=center, **field_parameters)
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py",
> line 1058, in __init__
>     self._refresh_data()
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py",
> line 320, in _refresh_data
>     self.get_data()
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py",
> line 859, in get_data
>     if self._generate_field(field):
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py",
> line 362, in _generate_field
>     self[field] = self.pf.field_info[field](self)
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/field_info_container.py",
> line 395, in __call__
>     dd = self._function(self, data)
>   File "cosmic_ray_fra.py", line 32, in my_new_field
>     if data.pf["MachNumber"] < 2:
>   File
> "/data1/pdf/csurajit/yt-x86_64/src/yt-hg/yt/data_objects/static_output.py",
> line 147, in __getitem__
>     raise KeyError(key)
> KeyError: 'MachNumber'

Yeah, that pretty much says that there's no such thing as
data.pf["MachNumber"]. Please try the derived field that I've suggested
in my previous mail.
Cheers,
Kacper

> 
> On Mon, Oct 21, 2013 at 2:58 PM, Kacper Kowalik <xarthisius.kk at gmail.com>wrote:
> 
>> On 10/21/2013 11:10 AM, Reju Sam John wrote:
>>> Dear all,
>>>
>>> I would like to create a derived field which should return a value
>>> according to specified conditions. My definition of new field is shown
>>> below.. But it is giving error.
>>>
>>>
>>> @derived_field(name = "MyField")
>>> def my_new_field(field, data):
>>>     if data.pf["MachNumber"] < 2 :
>>>         return (.5* (data["MachNumber"])**2) - 1
>>>     elif data.pf["MachNumber"] < 100 :
>>>         return (.5* (data["MachNumber"])**4) + (.5*
>> (data["MachNumber"])**3)
>>>     else:
>>>        return 5.446361E-01
>>>
>>>
>>>
>>> Please suggest me how to implement if, elif, else statements in creating
>> a
>>> derived field.
>>
>> Hi,
>> your derived fields looks fine (except for missing space in the
>> indentation of the last statement). Could you attach the backtrace?
>>
>> One thing that's confusing me is 'data.pf["MachNumber"]'. Do you have a
>> global parameter with such name defined or you'd rather create a MyField
>> based on local value of "MachNumber" field?
>> If the latter you could try something like this:
>>
>> @derived_field(name = "MyField")
>> def my_new_field(field, data):
>>     temp = data["MachNumber"].copy().fill(5.446361E-01)
>>     ind = np.where(data["MachNumber"] < 2)
>>     temp[ind] = 0.5 * data["MachNumber"][ind] ** 2 - 1.0
>>     ind = np.where((data["MachNumber"] >= 2) &
>>                    (data["MachNumber"]) < 100))
>>     temp[ind] = 0.5 * data["MachNumber"][ind] ** 4 + \
>>                 0.5 * data["MachNumber"][ind] ** 3
>>     return temp
>>
>>
>> Cheers,
>> Kacper
>>
>>
>>
>> _______________________________________________
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>> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>>
>>
> 
> 
> 
> 
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