[SciPy-User] Request for usage examples on scipy.stats.rv_continuous and scipy.ndimage.grey_dilate(structure)

Emmanuelle Gouillart emmanuelle.gouillart@normalesup....
Mon Mar 22 10:37:34 CDT 2010


Hi,

The documentation of ndimage.grey_dilate is much more detailed on the doc
wiki (including the use of structure, footprint etc.)
http://docs.scipy.org/scipy/docs/scipy.ndimage.morphology.grey_dilation/
(like most other functions of ndimage.morphology, the docstring has
been edited quite recently and the changes haven't made their way to the
"official" doc yet).

Cheers,

Emmanuelle

On Mon, Mar 22, 2010 at 03:44:41PM +0100, Christoph Deil wrote:
> Hi,

> I am having some trouble figuring out how to use the following two aspects of scipy:

> 1) How can I  create a random distribution given by some python formula, e.g. pdf(x) = x**2 in the range x = 1 to 2.

> The example given in the rv_continuous docstring doesn't work for me:
> In [1]: import matplotlib.pyplot as plt
> In [2]: numargs = generic.numargs
> AttributeError: type object 'numpy.generic' has no attribute 'numargs'

> Is it also possible to use rv_continuous for multidimensional distributions, say pdf(x,y)=x*y in the range x = 1 to 2 and y = 0 to 3?
> Or for pdfs that are just given numerically on a grid (say as the result of a gaussian_kde() ), not by a python function?

> It would be nice if someone could add a few examples that show rv_continuous usage to the docstring or tutorial.

> 2) How to use the 'structure' argument of scipy.ndimage.grey_dilate() correctly?
> There are some explanations at
> http://docs.scipy.org/doc/scipy/reference/tutorial/ndimage.html
> but I think they are inconsistent with the implementation:

> --------------------------------------------------------------
> In [98]: a = zeros((7,7)); a[3,3]=1; a
> Out[98]: 
> array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  1.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.]])
> In [100]: s = generate_binary_structure(2,2); s
> Out[100]: 
> array([[ True,  True,  True],
>        [ True,  True,  True],
>        [ True,  True,  True]], dtype=bool)

> In [101]: grey_dilation(a,size=(3,3))
> Out[101]: 
> array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.]])

> In [102]: grey_dilation(a,size=(3,3),structure=s)
> Out[102]: 
> array([[ 1.,  1.,  1.,  1.,  1.,  1.,  1.],
>        [ 1.,  1.,  1.,  1.,  1.,  1.,  1.],
>        [ 1.,  1.,  2.,  2.,  2.,  1.,  1.],
>        [ 1.,  1.,  2.,  2.,  2.,  1.,  1.],
>        [ 1.,  1.,  2.,  2.,  2.,  1.,  1.],
>        [ 1.,  1.,  1.,  1.,  1.,  1.,  1.],
>        [ 1.,  1.,  1.,  1.,  1.,  1.,  1.]])

> In [103]: grey_dilation(a,structure=s)
> ---------------------------------------------------------------------------
> TypeError                                 Traceback (most recent call last)

> /Users/deil/<ipython console> in <module>()

> /opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/scipy/ndimage/morphology.pyc in grey_dilation(input, size, footprint, structure, output, mode, cval, origin)
>     354             sz = footprint.shape[ii]
>     355         else:
> --> 356             sz = size[ii]
>     357         if not sz & 1:
>     358             origin[ii] -= 1

> TypeError: 'NoneType' object is unsubscriptable

> In [104]: grey_dilation(a,footprint=s)
> Out[104]: 
> array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  1.,  1.,  1.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.],
>        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.]])
> --------------------------------------------------------------

> Why doesn't  grey_dilation(a,structure=s) work?
> Why doesn't grey_dilation(a,size=(3,3),structure=s) give the same result as grey_dilation(a,size=(3,3),footprint=s)?

> I am running on numpy version 1.4.0 and scipy version 0.7.1

> Thanks!
> --Christoph



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