[yt-users] How to use if, elif, else statements in creating a derived field
Reju Sam John
rejusamjohn at gmail.com
Sat Oct 26 23:16:29 PDT 2013
Thanks nathan and suoqing..... Let me try with your suggestions....
On Sun, Oct 27, 2013 at 11:37 AM, Nathan Goldbaum <nathan12343 at gmail.com>wrote:
> And using suoqing's example, I can control whether or not we should take
> the logarithm of a variable in plots:
>
> @derived_field(name = "MyField", take_log=False)
> def my_new_field(field, data):
> tmp_data = (data["MachNumber"] <= 2) * (.5 * data["MachNumber"]**2. -
> 1)
> tmp_data = tmp_data + (data["MachNumber"] > 2) * (data["MachNumber"]
> <= 100) * ((.5* (data["MachNumber"])**4) + (.5* (data["MachNumber"])**3))
> tmp_data = tmp_data + (data["MachNumber"] > 100) * 5.446361E-01
> return tmp_data
>
> If you've already created a plot, you can also disable field logging like
> so:
>
> slc = SlicePlot(pf, 0, 'Density')
> slc.set_log('Density', False)
>
> -Nathan
>
>
> On Sat, Oct 26, 2013 at 11:02 PM, Suoqing JI <jisuoqing at gmail.com> wrote:
>
>> Hi Reju,
>>
>> The first thing occurs to me is that the area of white patch contains no
>> positive field value, so it can not be plotted in log scale.
>>
>> Also, about the way of defining a derived field, I might prefer the
>> following way, for example:
>>
>> @derived_field(name = "MyField")
>> def my_new_field(field, data):
>> tmp_data = (data["MachNumber"] <= 2) * (.5 * data["MachNumber"]**2. -
>> 1)
>> tmp_data = tmp_data + (data["MachNumber"] > 2) * (data["MachNumber"]
>> <= 100) * ((.5* (data["MachNumber"])**4) + (.5* (data["MachNumber"])**3))
>> tmp_data = tmp_data + (data["MachNumber"] > 100) * 5.446361E-01
>> return tmp_data
>>
>> Best wishes,
>> Suoqing
>>
>> On Oct 26, 2013, at 10:27 PM, Reju Sam John <rejusamjohn at gmail.com>
>> wrote:
>>
>> Dear Matt,
>> Thanks for the help. Now my problem with the code solved. But the slice
>> plot of the new field has some problem -- white patch are coming as shown
>> below. What may be the reason?
>> <output.png>
>>
>>
>> On Sat, Oct 26, 2013 at 7:59 PM, Matthew Turk <matthewturk at gmail.com>wrote:
>>
>>> Hi Reju,
>>>
>>> On Sat, Oct 26, 2013 at 2:50 AM, Reju Sam John <rejusamjohn at gmail.com>
>>> wrote:
>>> > Dear Kacper,
>>> >
>>> > My logic was wrong, and yours is right. But with the following code
>>> >
>>> > @derived_field(name = "MyField")
>>> > def my_new_field(field, data):
>>> > temp = data["MachNumber"].copy().fill(5.446361E-01)
>>> > #print temp
>>> >
>>> > ind = np.where(data["MachNumber"] < 2)
>>> > temp[ind] = 1.9564E-3*((data["MachNumber"][ind]**2) - 1)
>>> > ind = np.where((data["MachNumber"] >= 2) and (data["MachNumber"])
>>> < 100)
>>> > temp[ind] =
>>> >
>>> (5.699327E-1*((data["MachNumber"][ind]-1)**4))/(data["MachNumber"][ind]**4)
>>> > - (3.337557E-1*
>>> > ((data["MachNumber"][ind]-1)**3))/((data["MachNumber"][ind])**4) +
>>> > (4.173271E+0*
>>> > ((data["MachNumber"][ind]-1)**2))/((data["MachNumber"][ind])**4) -
>>> > (9.775620E+0*
>>> ((data["MachNumber"][ind]-1)))/((data["MachNumber"][ind])**4)+
>>> > 5.455605E+0/(data["MachNumber"][ind])**4
>>> > return temp
>>> >
>>> > I am getting this Traceback
>>> >
>>> > line 41, in my_new_field
>>> > temp[ind] = 1.9564E-3*((data["MachNumber"][ind]**2) - 1)
>>> > TypeError: 'NoneType' object does not support item assignment
>>> >
>>> > Would you suggest any solution?
>>>
>>> I believe the problem is in your .fill() statement. That doesn't
>>> return an array, so you need to do it after the assignment. For
>>> instance:
>>>
>>> temp = data["MachNumber"].copy()
>>> temp.fill(5.446361E-01)
>>>
>>> -Matt
>>>
>>> >
>>> >
>>> >
>>> > 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
>>> >>
>>> >>
>>> >>
>>> >> _______________________________________________
>>> >> yt-users mailing list
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>>> >> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>>> >>
>>> >
>>> >
>>> >
>>> > --
>>> > Reju Sam John
>>> >
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>>
>>
>>
>> --
>> Reju Sam John
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--
Reju Sam John
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