[NumPy-Tickets] [NumPy] #2208: chebval: subtract half of first coefficient?
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Sat Sep 1 11:47:17 CDT 2012
#2208: chebval: subtract half of first coefficient?
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Reporter: smeared ink | Owner: charris
Type: defect | Status: closed
Priority: normal | Milestone: 1.8.0
Component: numpy.polynomial | Version: devel
Resolution: invalid | Keywords: chebyshev chebval
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Changes (by charris):
* status: new => closed
* resolution: => invalid
Comment:
No. The reference you give determines the Chebyshev coefficients for
fitting a function using the Chebyshev points of the first kind over which
the Chebyshev polynomials are orthogonal, but not normalized. The factor
of N/2 shown at the link accounts for the lack of normalization except for
the T_0 term, which needs an extra factor of .5. Because the chebval
function evaluates series, you need to correct the c_0 coefficient
determined the NR way before calling chebval. Alternatively, you can fix
the normalization factor for the T_0 term up front if you are using a
matrix multiply to fit a large number of functions.
Perhaps I should add a function approximation method to the classes.
Hmm...
--
Ticket URL: <http://projects.scipy.org/numpy/ticket/2208#comment:1>
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