Re: [Numpy-discussion] convolve

[Robert K. <rk...@uc...>]

Alan G Isaac wrote:
> On Wed, 27 Jul 2005, Ren=E9 Bastian apparently wrote:=20
>=20
>>Outcommenting
>>if len(data) < len(kernel):
>>   data, kernel =3D kernel, data
>>in convolve.py gives the correct result.=20
>=20
> The author is not listed for this numarray module,
> so we cannot directly ask why this behavior was chosen.

This behavior was chosen for performance reasons. Since convolution is=20
commutative, it doesn't matter what order the arguments come in. I do=20
not see the behavior Ren=E9 is claiming. Perhaps Ren=E9 can tell us what=20
version of numarray he is using? or provide an example? I am using CVS=20
as of a week ago, I think.

In [10]: import numarray

In [11]: import numarray.convolve

In [12]: a =3D numarray.arange(10) + 1.

In [13]: b =3D numarray.arange(5) + 2.

In [14]: c =3D a - 1.

In [15]: numarray.convolve.convolve(a,b)
Out[15]:
array([   2.,    7.,   16.,   30.,   50.,   70.,   90.,  110.,  130.,
         150.,  148.,  133.,  104.,   60.])

In [16]: numarray.convolve.convolve(b,a)
Out[16]:
array([   2.,    7.,   16.,   30.,   50.,   70.,   90.,  110.,  130.,
         150.,  148.,  133.,  104.,   60.])

In [17]: numarray.convolve.convolve(a,c)
Out[17]:
array([   0.,    1.,    4.,   10.,   20.,   35.,   56.,   84.,  120.,
         165.,  210.,  244.,  266.,  275.,  270.,  250.,  214.,  161.,
          90.])

In [18]: numarray.convolve.convolve(c,a)
Out[18]:
array([   0.,    1.,    4.,   10.,   20.,   35.,   56.,   84.,  120.,
         165.,  210.,  244.,  266.,  275.,  270.,  250.,  214.,  161.,
          90.])

--=20
Robert Kern
rk...@uc...

"In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die."
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