Re: [Numpy-discussion] Possible bug in Numpy.convolve

2017-03-22 Thread Thøger Emil Rivera-Thorsen 

OK, this is embarrassing.
I had in fact made the kernel only almost symmetric, it was slightly 
offset to one side.

This caused it. Only a wetware bug.
Sorry for having wasted your time!


On 03/23/2017 03:38 AM, josef.p...@gmail.com wrote:



On Wed, Mar 22, 2017 at 10:06 PM, Thøger Emil Rivera-Thorsen 
> wrote:


Dear list;

I am honestly not certain whether this, or the SciPy list, is the
appropriate place to post this; please let me know if I got it wrong.

I am convolving a 1D data set containing a relatively narrow peak,
with a relatively narrow Gaussian kernel, in order to emulate the
effect of atmospheric seeing on astrophysical observations.

I have a 1D data array 45 pixels long, and a Gaussian kernel, and
run np.convolve(data, kernel, mode='same') on the two arrays, the
resulting array's peak is shifted relative to the origin. I have
attached a plot to illustrate.

The original data is shown in blue. When I convolve it with a
symmetric kernel (black), I get an offset resulting peak
(magenta). If I flip the kernel -- even though it is perfectly
symmetric -- the resulting curve is offset in the opposite
direction (yellow). However, if I offset the kernel so it is
centered exactly one pixel below the central value, the output
array gets centered correct (red), even if I flip the (now no
longer symmetric) kernel.

This is using Numpy 1.11.3, python 2.7.13, on Anaconda 4.3.0
64-bit on Ubuntu 16.10

Using astropy.convolution, reproduces the correct red curve, so I
can use that for now, but it seems to me this is either a bug or,
if it is indeed the intended behavior, a word of caution would be
merited in the docstring.

Cheers,

Emil Rivera-Thorsen



___
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org 
https://mail.scipy.org/mailman/listinfo/numpy-discussion



Can you provide an example to replicate?

I haven't seen this behavior, it looks centered to me, at least for 
odd window length..
AFAIR, I had to try a bit in the past for how to set the window and 
location with even window length.


>>> np.__version__
'1.11.2'

>>> x = np.linspace(-1, 1, 21)
>>> w = stats.norm.pdf(np.linspace(-3, 3, 5))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ -2.e-01,  -1.33368234e-01],
   [ -1.e-01,  -6.66841169e-02],
   [  0.e+00, 1.51788304e-17],
   [  1.e-01, 6.66841169e-02],
   [  2.e-01, 1.33368234e-01]])


>>> x = np.abs(np.linspace(-1, 1, 21))
>>> w = stats.norm.pdf(np.linspace(-3, 3, 4))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ 0.2   ,  0.12320129],
   [ 0.1   ,  0.07392077],
   [ 0.,  0.02552663],
   [ 0.1   ,  0.02552663],
   [ 0.2   ,  0.07392077]])


>>> w = stats.norm.pdf(np.linspace(-3, 3, 5))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ 0.2   ,  0.13336823],
   [ 0.1   ,  0.06757049],
   [ 0.,  0.02767626],
   [ 0.1   ,  0.06757049],
   [ 0.2   ,  0.13336823]])

Josef


___
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
https://mail.scipy.org/mailman/listinfo/numpy-discussion



___
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
https://mail.scipy.org/mailman/listinfo/numpy-discussion

Re: [Numpy-discussion] Possible bug in Numpy.convolve

2017-03-22 Thread josef . pktd 
On Wed, Mar 22, 2017 at 10:06 PM, Thøger Emil Rivera-Thorsen <
thoger.e...@gmail.com> wrote:

> Dear list;
>
> I am honestly not certain whether this, or the SciPy list, is the
> appropriate place to post this; please let me know if I got it wrong.
>
> I am convolving a 1D data set containing a relatively narrow peak, with a
> relatively narrow Gaussian kernel, in order to emulate the effect of
> atmospheric seeing on astrophysical observations.
>
> I have a 1D data array 45 pixels long, and a Gaussian kernel, and run
> np.convolve(data, kernel, mode='same') on the two arrays, the resulting
> array's peak is shifted relative to the origin. I have attached a plot to
> illustrate.
>
> The original data is shown in blue. When I convolve it with a symmetric
> kernel (black), I get an offset resulting peak (magenta). If I flip the
> kernel -- even though it is perfectly symmetric -- the resulting curve is
> offset in the opposite direction (yellow). However, if I offset the kernel
> so it is centered exactly one pixel below the central value, the output
> array gets centered correct (red), even if I flip the (now no longer
> symmetric) kernel.
>
> This is using Numpy 1.11.3, python 2.7.13, on Anaconda 4.3.0 64-bit on
> Ubuntu 16.10
>
> Using astropy.convolution, reproduces the correct red curve, so I can use
> that for now, but it seems to me this is either a bug or, if it is indeed
> the intended behavior, a word of caution would be merited in the docstring.
>
> Cheers,
>
> Emil Rivera-Thorsen
>
>
>
> ___
> NumPy-Discussion mailing list
> NumPy-Discussion@scipy.org
> https://mail.scipy.org/mailman/listinfo/numpy-discussion
>
>
Can you provide an example to replicate?

I haven't seen this behavior, it looks centered to me, at least for odd
window length..
AFAIR, I had to try a bit in the past for how to set the window and
location with even window length.

>>> np.__version__
'1.11.2'

>>> x = np.linspace(-1, 1, 21)
>>> w = stats.norm.pdf(np.linspace(-3, 3, 5))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ -2.e-01,  -1.33368234e-01],
   [ -1.e-01,  -6.66841169e-02],
   [  0.e+00,   1.51788304e-17],
   [  1.e-01,   6.66841169e-02],
   [  2.e-01,   1.33368234e-01]])


>>> x = np.abs(np.linspace(-1, 1, 21))
>>> w = stats.norm.pdf(np.linspace(-3, 3, 4))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ 0.2   ,  0.12320129],
   [ 0.1   ,  0.07392077],
   [ 0.,  0.02552663],
   [ 0.1   ,  0.02552663],
   [ 0.2   ,  0.07392077]])


>>> w = stats.norm.pdf(np.linspace(-3, 3, 5))
>>> np.column_stack((x, np.convolve(x, w, mode='same')))[8:13]
array([[ 0.2   ,  0.13336823],
   [ 0.1   ,  0.06757049],
   [ 0.,  0.02767626],
   [ 0.1   ,  0.06757049],
   [ 0.2   ,  0.13336823]])

Josef
___
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
https://mail.scipy.org/mailman/listinfo/numpy-discussion

[Numpy-discussion] Possible bug in Numpy.convolve

2017-03-22 Thread Thøger Emil Rivera-Thorsen 

Dear list;

I am honestly not certain whether this, or the SciPy list, is the 
appropriate place to post this; please let me know if I got it wrong.


I am convolving a 1D data set containing a relatively narrow peak, with 
a relatively narrow Gaussian kernel, in order to emulate the effect of 
atmospheric seeing on astrophysical observations.


I have a 1D data array 45 pixels long, and a Gaussian kernel, and run 
np.convolve(data, kernel, mode='same') on the two arrays, the resulting 
array's peak is shifted relative to the origin. I have attached a plot 
to illustrate.


The original data is shown in blue. When I convolve it with a symmetric 
kernel (black), I get an offset resulting peak (magenta). If I flip the 
kernel -- even though it is perfectly symmetric -- the resulting curve 
is offset in the opposite direction (yellow). However, if I offset the 
kernel so it is centered exactly one pixel below the central value, the 
output array gets centered correct (red), even if I flip the (now no 
longer symmetric) kernel.


This is using Numpy 1.11.3, python 2.7.13, on Anaconda 4.3.0 64-bit on 
Ubuntu 16.10


Using astropy.convolution, reproduces the correct red curve, so I can 
use that for now, but it seems to me this is either a bug or, if it is 
indeed the intended behavior, a word of caution would be merited in the 
docstring.


Cheers,

Emil Rivera-Thorsen


___
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
https://mail.scipy.org/mailman/listinfo/numpy-discussion