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

Christoph Deil Deil.Christoph@googlemail....
Mon Mar 22 09:44:41 CDT 2010


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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