> On Thu, Jun 30, 2011 at 11:32 AM, Thomas K Gamble
>
> <
tkgamble@windstream.net>wrote:
> > I'm trying to convert some IDL code to python/numpy and i'm having some
> > trouble understanding the rules for boradcasting during some operations.
> > example:
> >
> > given the following arrays:
> > a = array((2048,3577), dtype=float)
> > b = array((256,25088), dtype=float)
> > c = array((2048,3136), dtype=float)
> > d = array((2048,3136), dtype=float)
> >
> > do:
> > a = b * c + d
> >
> > In IDL, the computation is done without complaint and all array sizes are
> > preserved. In ptyhon I get a value error concerning broadcasting. I can
> > force it to work by taking slices, but the resulting size would be a =
> > (256x3136) rather than (2048x3577). I admit that I don't understand IDL
> > (or
> > python to be honest) well enough to know how it handles this to be able
> > to replicate the result properly. Does it only operate on the smallest
> > dimensions ignoring the larger indices leaving their values unchanged?
> > Can someone explain this to me?
>
> I don't see a problem
>
> In [1]: datetime64('now')
> Out[1]: numpy.datetime64('2011-07-01T07:18:35-0600')
>
> In [2]: a = array((2048, 3577), float)
>
> In [3]: b = array((256, 25088), float)
>
> In [4]: c = array((2048, 3136), float)
>
> In [5]: d = array((2048, 3136), float)
>
> In [6]: a = b*c + d
>
> In [7]: a
> Out[7]: array([ 526336., 78679104.])
>
> What is the '*' in your expression supposed to mean?