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

21 Oct 2013


      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@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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