Floating-point glitches with the math module. Bug? Or am I missing something?
Wed Sep 22 23:07:17 CEST 2004
Alexandre Fayolle <alf at merlin.fayauffre.org> writes:
> Firstly, I use the fact that scipy provides a cosm1 function which
> returns cos(x)-1, and which is more precise that for small values of x.
The simple approximation is cos(x)-1 = -x**2/2. Fancier approximation
is cos(x)-1 = -x**2/2 + x**4/24, which should exceed machine precision
for x < 2**-12 or so.
> Then I'd like to use an acosm1 function in order to keep the precision.
> Since there is no such function available, I'll just solve
> cosm1(x)-cos_gamma_minus_1=0 for which I know there is a solution
acosm1(x) = sqrt(-2*x) for the simple approximation. Use quadratic
formula to solve the fancier one.
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