Hi all: I also have noticed bad results with convolveND when it used the
FFT path. What I got for some input data was all NaNs, whereas the direct
method gave reasonable results.
Another bug I noticed was that the 'truncate' option is not setting bad
values correctly near the boundaries (from the convolveND man page):
The (default) truncate option marks all the near-boundary pixels as
BAD if you have bad values compiled into your PDL and the array's
badflag is set.
I ended up having to manually set bad values at the start and end of the
input array.
Regards,
Doug
[email protected]
Software Engineer IV
UCAR - COSMIC, Tel. (303) 497-2611
On Fri, 20 Feb 2009, hernan gonzalez wrote:
> fftconvolve seems indeed broken.
>
> my $p1 = pdl(1,0,0,0);
> my $p2 = pdl(1,0,0,0);
> fftconvolve($p1,$p2);
> print $p1 . "\n";
>
> results in
>
> [1.75 -0.25 -0.25 -0.25]
>
>
> It seems that the result is missing the DC component (as if the fft
> had supressed the 0-freq value) and a factor 2 is missing somewhere.
>
> Hern?n
>
>
>> Andreas Michalowski michalowski at ifsw.uni-stuttgart.de
>
> A simple example is like this: I convolve two 1D piddles, the first is
> zero except for one value which is 1. The second one has a gaussian
> shape. I expect as the result a piddle which contains a gaussian shape
> converging to zero far away from the center.
>
> The resulting piddle shows the expected gaussian shape but is not
> converging to zero, instead of that to a negative constant value. It
> seems that the result has a negative offset.
> If I do the convolution with "convolve" instead of "fftconvolve" the
> result is exactly what I expect.
>
> Does someone has an idea why fftconvolve has this (for me) unexpected
> and (for me) incorrect behavior?
>
> Many thanks!
>
> Andreas
>
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