Fri Feb 1 08:50:21 CST 2013
On Fri, Feb 1, 2013 at 9:23 AM, François Boulogne <firstname.lastname@example.org> wrote:
> I need to deconvolve a signal with a filter. I had a look in the
> documentation. The function exists but the docstring is missing and I'm
> not satisfied of the result I got from a "simple" example.
> filter = np.array([0,1,1,1,1,0])
> step = np.array([0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1])
> # I convolve both
> res = convolve(step, filter, 'valid')
> # and it returns a slope as expected
> array([0, 0, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4])
> Now, I want to deconvolve.
> deconvolve(res, filter)
> # oops, it raises an exception
> ValueError: BUG: filter coefficient a == 0 not supported yet
> # well, let's try this
> deconvolve(res, filter+1e-9)
> (array([ 0.00000000e+00, 0.00000000e+00, 1.00000000e+09,
> -9.99999999e+17, 9.99999999e+26, -9.99999999e+35,
> 9.99999999e+44, -9.99999999e+53, 9.99999999e+62,
> -9.99999999e+71, 9.99999999e+80, -9.99999999e+89]),
> array([ 0.00000000e+00, 0.00000000e+00, 1.11022302e-16,
> -8.27130862e-08, -4.42500000e+01, 5.46901335e+10,
> 8.27266814e+19, 7.56858250e+28, -8.74285726e+37,
> 9.99419626e+46, 8.27205507e+55, -8.26933326e+64,
> 9.99999999e+89, 9.99999999e+89, 9.99999999e+89,
> 1.00000000e+90, 9.99999999e+80]))
> It's better but I do not recognize my signal :)
> 1/ Am I misunderstanding or missing something?
> 2/ How can I do it correctly?
not supported, maybe using the numpy polynomial might work for the deconvolution
from the docstring of lfilter, which is used by deconvolve:
a : array_like
The denominator coefficient vector in a 1-D sequence. If ``a``
is not 1, then both `a` and `b` are normalized by ``a``.
with the normalization your 1e-9 blows up the calculations.
(it's been a long time since I tried to figure out deconvolve, and I
always had 1 in the first position)
> I also noted that no test exists for deconvolve() :(
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