[Numpy-discussion] Re: numpy.sin
Robert Kern
robert.kern at gmail.com
Thu May 25 12:29:06 EDT 2006
Alan G Isaac wrote:
> On Thu, 25 May 2006, Robert Kern apparently wrote:
>>That your demonstration results in the desired exact 0.0
>>for multiples of 2*pi is an accident. The results for
>>values other than integer multiples of pi will be as wrong
>>or more wrong.
>
> It seems that a continuity argument should undermine that as
> a general claim. Right?
What continuity? This is floating-point arithmetic.
[~]$ bc -l
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
scale = 50
s(1000000)
-.34999350217129295211765248678077146906140660532871
[~]$ python
Python 2.4.1 (#2, Mar 31 2005, 00:05:10)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1666)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from numpy import *
>>> sin(1000000.0)
-0.34999350217129299
>>> sin(1000000.0 % (2*pi))
-0.34999350213477698
>>>
> But like I said: I was just wondering if there was anything
> exploitable here.
Like I said: not really.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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