[yt-users] derived quantities

[Matthew Turk]

Hi Stephen,

I have now opened up derived_quantities and inspected.  By searching
for n_ret=1, which seems to be what you are looking for, I was able to
identify the AngularMomentumVector quantity also has only one return
value.  In that source code it returns an iterable of length 1.  Based
on this, I am going to suggest:

return [ct.sum(),]

Because the derived quantity machinery goes to great lengths to
preserve some of its memory conservation and processr independence,
the source is usually a good place to look for examples and so on.
What happens is that the DQ function must return an iterable.  When
you first returned ct, it was an iterable: so it worked.  However,
because you told it to only take one value, it only took the leading
value.  Now, returning ct.sum(), you are no longer providing an
iterable, so it dies.  Returning it *as* an iterable with only one
important element should fix this issue.

-Matt

On Fri, Dec 10, 2010 at 4:06 PM, Stephen Skory <stephenskory at yahoo.com> wrote:
> Matt,
>
>> But, I think you should be returning ct.sum() from _NumberOfStars.
>
>
> With only that change to what I previously sent, I get this...
>
>
> Traceback (most recent call last):
>  File "analyze.py", line 19, in <module>
>    print 'total', dd.quantities["NumberOfStars"]()
>  File "/share/home/00649/tg457850/yt/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/data_objects/derived_quantities.py", line 90, in __call__
>    return self._call_func_lazy(args, kwargs)
>  File "/share/home/00649/tg457850/yt/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/data_objects/derived_quantities.py", line 98, in _call_func_lazy
>    for i in range(self.n_ret): self.retvals[i].append(rv[i])
> IndexError: invalid index to scalar variable.
>
>  Stephen Skory
> stephenskory at yahoo.com
> http://stephenskory.com/
> 510.621.3687 (google voice)
> _______________________________________________
> yt-users mailing list
> yt-users at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>