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

[Reju Sam John]

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?
[image: Inline image 1]


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
> >> yt-users at lists.spacepope.org
> >> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
> >>
> >
> >
> >
> > --
> > Reju Sam John
> >
> > _______________________________________________
> > yt-users mailing list
> > yt-users at lists.spacepope.org
> > http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
> >
> _______________________________________________
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>



-- 
Reju Sam John
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