[Numpy-discussion] Re: sum and mean methods behaviour

[Perry Greenfield]

Peter Verveer writes:
> Todd Miller writes:
> > 1. Add a type parameter to sum which defaults to widest type.
> >
> > 2. Add a type parameter to reductions (and fix output type handling).
> > Default is same-type as it is now.  No major changes to C-code.
> >
> > 3. Add a WidestType(array) function:
> >
> >         Bool                        --> Bool
> >         Int8,Int16,Int32,Int64      --> Int64
> >         UInt8, UInt16,UInt32,UInt64 --> UInt64 (Int64 on win32)
> >         Float32, Float64            --> Float64
> >         Complex32, Complex64        --> Complex64
>
> This sounds like a good solution.
>
> > The only thing this really leaves out, is a higher performance
> > implementation of sum/mean which Peter referred to a few times.
>
> Is this really the case? It depends on how you plan to implement
> the output
> conversion. If you will do this by allocating a temporary
> converted copy of
> the complete input before the calculations then this potentially
> requires a
> lot of temporary storage. But it is certainly possible to come up with an
> implementation that avoids this. Have you given this some thought?
>
The way numarray ufuncs currently work is that for larger arrays,
the conversion of types is only done in blocks. No temporary copy is
made of the whole input array. So the temporary storage issue is not
a problem.