[Numpy-discussion] type of matrixmultiply result

[Todd Miller]

On Thu, 2004-06-24 at 11:08, Perry Greenfield wrote:
> Rick White wrote:
> 
> > On 24 Jun 2004, Todd Miller wrote:
> > 
> > > On Thu, 2004-06-24 at 06:14, Curzio Basso wrote:
> > >
> > > > I noticed that when multiplying two matrices of type Float32, 
> > the result
> > > > is Float64:
> > >
> > > I modified dot() and innerproduct() this morning to return Float32 and
> > > Complex32 for like inputs.
> > 
> > I wonder whether it would be worth providing an option to accumulate
> > the sums using Float64 and to convert to Float32 before storing them in
> > an array.  I suspect that one reason this returned Float64 is that it
> > is very easy to run into precision/roundoff problems in
> > single-precision matrix multiplies.  You could avoid that by using
> > doubles for the sum while still returning the result as a single.
> > 				Rick
> > 
> I definitely agree. I'm pretty certain the reason it was done
> with double precision floats is the sensitivity to roundoff
> issues with matrix operations. I think Rick is right though that
> only intermediate calculations need to be done in double precision
> and that doesn't require the whole output array to be kept that way.
> 
> Perry 

OK.  I implemented intermediate sums using Float64 and Complex64 but
single precision inputs will still result in single precision outputs. 

Todd