[SciPy-user] how to make a sinc(x) function - "divide by zero" !

Sebastian Haase haase at msg.ucsf.edu
Mon Dec 12 11:32:47 CST 2005


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 ?
Thanks,
Sebastian Haase


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