[Numpy-discussion] polynomial with negative exponents
gregor.thalhammer at gmail.com
Mon Dec 12 12:17:35 EST 2011
Am 12.12.2011 um 15:04 schrieb LASAGNA DAVIDE:
> I have written a class for polynomials with negative
> exponents like:
> p(x) = a0 + a1*x**-1 + ... + an*x**-n
> The code is this one:
> class NegativeExpPolynomial( object ):
> def __init__ ( self, coeffs ):
> self.coeffs = np.array( coeffs )
> def __call__( self, x ):
> return sum( (c*x**(-i) for i, c in enumerate(
> self.coeffs ) ) )
> where coeffs = [a0, a1, ..., an].
> I find that the way i evaluate the polynomial is kind of
> *slow*, especially for polynomial with order larger than
> ~200 and for arrays x large enough.
I fear that such high orders create a lot of troubles since evaluating them is very sensitive to numerical errors.
> Do you have suggestions on how to speed up this code?
Your polynomials with negative exponents are equivalent to a polynomial with positive exponents, but evaluated at 1/x. Therefore you can make use of the efficient polynomial functions of numpy. Try
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