Re[2]: [Numpy-discussion] Re: numpy.sin

[Alan G I. <ai...@am...>]

On Thu, 25 May 2006, Alexander Belopolsky apparently wrote: 
> This is not really a numpy issue, but general floating point problem. 
> Consider this: 
>>>> x=linspace(0,10*pi,11) 
>>>> all(array(map(math.sin, x))==sin(x)) 
> True 

I think this misses the point.
I was not suggesting numpy results differ from the C math library results.

>>> x1=sin(linspace(0,10*pi,21))
>>> x2=sin(linspace(0,10*pi,21)%(2*pi))
>>> all(x1==x2)
False
>>> x1
array([  0.00000000e+00,   1.00000000e+00,   1.22460635e-16,
        -1.00000000e+00,  -2.44921271e-16,   1.00000000e+00,
         3.67381906e-16,  -1.00000000e+00,  -4.89842542e-16,
         1.00000000e+00,   6.12303177e-16,  -1.00000000e+00,
        -7.34763812e-16,   1.00000000e+00,   8.57224448e-16,
        -1.00000000e+00,  -9.79685083e-16,   1.00000000e+00,
         1.10214572e-15,  -1.00000000e+00,  -1.22460635e-15])
>>> x2
array([  0.00000000e+00,   1.00000000e+00,   1.22460635e-16,
        -1.00000000e+00,   0.00000000e+00,   1.00000000e+00,
         1.22460635e-16,  -1.00000000e+00,   0.00000000e+00,
         1.00000000e+00,   1.22460635e-16,  -1.00000000e+00,
         0.00000000e+00,   1.00000000e+00,   1.22460635e-16,
        -1.00000000e+00,   0.00000000e+00,   1.00000000e+00,
         1.22460635e-16,  -1.00000000e+00,   0.00000000e+00])


I'd rather have x2:
I'm just asking if there is anything exploitable here.
Robert suggests not.

Cheers,
Alan Isaac