[SciPy-dev] numpy.broadcast
Robert Kern
robert.kern@gmail....
Wed Aug 5 16:01:32 CDT 2009
On Wed, Aug 5, 2009 at 15:40, David Goldsmith<d_l_goldsmith@yahoo.com> wrote:
> --- On Wed, 8/5/09, David Goldsmith <d_l_goldsmith@yahoo.com> wrote:
>
>> > It is necessarily == D. Broadcasting is associative.
>> > The
>> > (x*y*z).shape
>> > == (x*(y*z)).shape == ((x*y)*z).shape.
>
> Um:
>
>>>> x = np.array((1, 2, 3))
>>>> y = np.array([[4], [5], [6]])
>>>> z = x * y
>>>> x; y; z
> array([1, 2, 3])
> array([[4],
> [5],
> [6]])
> array([[ 4, 8, 12],
> [ 5, 10, 15],
> [ 6, 12, 18]])
>>>> B = np.broadcast
>>>> X = B(x, y, z)
>>>> Y = B(x, B(y, z))
>>>> Z = B(B(x, y), z)
>>>> X.numiter, Y.numiter, Z.numiter
> (3, 2, 2)
>>>> X.nd, Y.nd, Z.nd
> (2, 1, 2)
>>>> X.shape, Y.shape, Z.shape
> ((3, 3), (3,), (3, 3))
>
> Am I doing something wrong?
You are passing a broadcast iterator as an argument to broadcast. The
broadcast iterator iterates over the inputs in-parallel. This is
entirely different from actually operating on the inputs.
In [1]: x = array([1, 2, 3])
In [2]: y = array([[4], [5], [6]])
In [3]: z = x * y
In [4]: x*y*z
Out[4]:
array([[ 16, 64, 144],
[ 25, 100, 225],
[ 36, 144, 324]])
In [5]: (x*y)*z
Out[5]:
array([[ 16, 64, 144],
[ 25, 100, 225],
[ 36, 144, 324]])
In [6]: x*(y*z)
Out[6]:
array([[ 16, 64, 144],
[ 25, 100, 225],
[ 36, 144, 324]])
In [8]: array(list(broadcast(x,y)))
Out[8]:
array([[1, 4],
[2, 4],
[3, 4],
[1, 5],
[2, 5],
[3, 5],
[1, 6],
[2, 6],
[3, 6]])
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
-- Umberto Eco
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