Should numpy.sqrt(-1) return 1j rather than nan?

Sebastian Haase haase at msg.ucsf.edu
Thu Oct 12 13:30:34 CDT 2006


Hi,
On Thursday 12 October 2006 10:49, Christopher Barker wrote:
> As someone on this list (sorry to quick with the delete button) said:
<snip>

I think I might agree with everything (!) you that - very well written .

> Travis Oliphant wrote:
> > Now, it would be possible to give ufuncs a dtype keyword argument that
> > allowed you to specify which underlying loop was to be used for the
> > calculation.
> >
> > sqrt(a, dtype=complex).
>
> I like this OK, and isn't is similar to the dtype argument in the
> accumulating methods? (sum, etc.). However, it's probably not worth the
> C-api change -- is it that different than calling:
>
> sqrt(a.astype(complex)) ?
>

It is very late in the game - obvious ! (one week before the announced final 
release).  But I think adding the dtype argument to ufuncs would be a very 
useful addition !! 
It is very nice to look at ! And it saves (temporary) memory and should be 
noticeably faster than "sqrt(a.astype(complex))".

This dtype addition might address  many of the issues I have raised before on 
this list.

Travis,  be courageous  and change the C-API one last time before putting it 
in stone for 1.0 final !!!


> As for scipy, I heartily agree that scipy should be a superset of numpy,
> and NOT change the behavior of numpy functions and methods. We're taking
> the opportunity at this point for numpy to break backward compatibility
> with Numeric/numarray -- this is probably the best time to   do the same
> for scipy.
>
> couldn't we at least introduce new names?
>
> numpy.scimath.csqrt()
>
> for instance?
>
> -Chris
It has to be very well documented what the 12 functions (the last 3%) are were 
scipy and numpy differ.  --- if at all possible I would prefer a name change 
like csqrt (or better sqrtc - I always like seen things together when sorted 
alphabetically ;-) )     [by the way: I like sqrt(-1) == nan  just fine]

Thanks for the great work. 
- Sebastian

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