[SciPy-user] how to make a sinc(x) function - "divide by zero" !
sransom at nrao.edu
Mon Dec 12 12:04:16 CST 2005
Here is a simple version that I use. It uses the Taylor
expansion when the argument is near zero. Note that this
is using Numeric and umath right now. This should be
trivial to change to new scipy_core (which I am not using yet):
Return the sinc function [i.e. sin(pi * xs)/(pi * xs)]
for the values xs.
pxs = umath.pi*xs
On Monday 12 December 2005 12:39 pm, Arnd Baecker wrote:
> On Mon, 12 Dec 2005, Sebastian Haase wrote:
> > Hi,
> > I was trying to implement a "sinc" [sin(x)/x] in numarray. But the
> > "where"-semantics makes it choke on the x=0: 0/0 case.
> > (This should of course work for x being an array - so "if" is no
> > option) The best I could come up with was:
> > def sinc(r):
> > na.Error.pushMode(all="ignore")
> > a = na.where(r, na.divide(na.sin(r),r), 1)
> > na.Error.popMode()
> > return a
> > but I still seem to get a warning...
> > >>> F.sinc(0)
> > Warning: Encountered invalid numeric result(s) in divide
> > 1.0
> > What is a better way of doing this ?
> Yuo could try to use `vectorize` (warning: untested code)
> def sinc(x):
> if x==0.0: # presumably better to check for small
> x return 0.0 # here ...
> return sin(x)/x
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Scott M. Ransom Address: NRAO
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