[Numpy-discussion] strange seterr persistence between sessions

John Hunter jdh2358@gmail....
Mon Jul 28 14:56:18 CDT 2008


On Mon, Jul 28, 2008 at 2:35 PM, Robert Kern <robert.kern@gmail.com> wrote:

> Both, if the behavior exhibits itself without the npy file. If it only
> exhibits itself with an npy involved, then we have some more
> information about where the problem might be.

OK, I'll see what I can come up with.  In the mean time, as I was
trying to strip out the npy component and put the data directly into
the file, I find it strange that I am getting a floating point error
on this operation

  import numpy as np
  np.seterr("raise")
  import numpy.ma as ma

  x = 1.50375883
  m = ma.MaskedArray([x])
  sinc_alpha_ma = ma.sin(m) / m

---------------------------------------------------------------------------
FloatingPointError                        Traceback (most recent call last)

/home/jdhunter/<ipython console> in <module>()

/home/jdhunter/dev/lib64/python2.5/site-packages/numpy/ma/core.pyc in
__div__(self, other)
   1885     def __div__(self, other):
   1886         "Divide other into self, and return a new masked array."
-> 1887         return divide(self, other)
   1888     #
   1889     def __truediv__(self, other):

/home/jdhunter/dev/lib64/python2.5/site-packages/numpy/ma/core.pyc in
__call__(self, a, b)
    636         d1 = getdata(a)
    637         d2 = get_data(b)
--> 638         t = narray(self.domain(d1, d2), copy=False)
    639         if t.any(None):
    640             mb = mask_or(mb, t)

/home/jdhunter/dev/lib64/python2.5/site-packages/numpy/ma/core.pyc in
__call__(self, a, b)
    411         if self.tolerance is None:
    412             self.tolerance = np.finfo(float).tiny
--> 413         return umath.absolute(a) * self.tolerance >= umath.absolute(b)
    414 #............................
    415 class _DomainGreater:

FloatingPointError: underflow encountered in multiply

I am no floating point expert, but I don't see why a numerator of
0.99775383 and a denominator of 1.50375883 should be triggering an
underflow error.  It looks more like a bug in the ma core logic since
umath.absolute(a) * self.tolerance is more or less guaranteed to fail
if np.seterr("raise") is set

JDH


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