[Numpy-discussion] Asymmetry in Chebyshev.deriv v. Chebyshev.integ

David Goldsmith d.l.goldsmith@gmail....
Fri Apr 2 12:27:32 CDT 2010


On Thu, Apr 1, 2010 at 6:42 PM, David Goldsmith <d.l.goldsmith@gmail.com>wrote:

> >>> np.version.version
> '1.4.0'
> >>> c = np.polynomial.chebyshev.Chebyshev(1)
> >>> c.deriv(1.0)
> Chebyshev([ 0.], [-1.,  1.])
> >>> c.integ(1.0)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "<string>", line 441, in integ
>   File "C:\Python26\lib\site-packages\numpy\polynomial\chebyshev.py", line
> 739,
> in chebint
>     k = list(k) + [0]*(m - len(k))
> TypeError: can't multiply sequence by non-int of type 'float'
> >>> c.integ(1)
> Chebyshev([ 0.,  1.], [-1.,  1.])
>
> i.e., deriv accepts int_like input but integ doesn't.
>
> Given the way I just embarrassed myself on the scipy-dev list :-(, I'm
> confirming this is a bug before I file a ticket.
>

Also:

>>> c.deriv(0)
Chebyshev([ 1.], [-1.,  1.])
>>> c.integ(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 441, in integ
  File "C:\Python26\lib\site-packages\numpy\polynomial\chebyshev.py", line
729,
in chebint
    raise ValueError, "The order of integration must be positive"
ValueError: The order of integration must be positive

i.e., deriv supports zero-order differentiation, but integ doesn't support
zero-order integration (though I acknowledge that this may be a feature, not
a bug).

-- 
Mathematician: noun, someone who disavows certainty when their uncertainty
set is non-empty, even if that set has measure zero.
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