#10042: Doctest failure in sage/rings/polynomial/polynomial_element.pyx
-----------------------+----------------------------------------------------
Reporter: mpatel | Owner: mvngu
Type: defect | Status: needs_info
Priority: blocker | Milestone: sage-4.6
Component: doctest | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-----------------------+----------------------------------------------------
Comment(by kcrisman):
Replying to [comment:10 zimmerma]:
> Karl-Dieter, please could you isolate the problem (see instructions in
comment 4)? In particular we need to know if the problem lies in NumPy
itself, or in the RR<->NumPy conversion.
>
Like Dave, I don't have time to do much with this. Apparently something
goes 'wrong' in ?RealField, based on what I see here:
{{{
----------------------------------------------------------------------
| Sage Version 4.6.alpha2, Release Date: 2010-09-29 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
**********************************************************************
* *
* Warning: this is a prerelease version, and it may be unstable. *
* *
**********************************************************************
sage: R.<x> = RealField(200)[]
sage: f = x^2 - R(pi)
sage: f.roots(algorithm='numpy')
/Users/student/Desktop/sage-4.6.alpha2/local/bin/sage-ipython:1:
UserWarning: NumPy does not support arbitrary precision arithmetic. The
roots found will likely have less precision than you expect.
#!/usr/bin/env python
[(-1.7724538509055161039640324815991334617137908935546875000000, 1),
(1.7724538509055158819194275565678253769874572753906250000000, 1)]
sage: seq=[]
sage: K = f.parent().base_ring()
sage: L = K
sage: K
Real Field with 200 bits of precision
sage: input_fp = True
sage: L
Real Field with 200 bits of precision
sage: output_fp=True
sage: input_complex=False
sage: output_complex=False
sage: input_arbprec=True
sage: import numpy
sage: from numpy.linalg.linalg import LinAlgError
sage: coeffs = f.list()
sage: coeffs
[-3.1415926535897932384626433832795028841971693993751058209749,
0.00000000000000000000000000000000000000000000000000000000000,
1.0000000000000000000000000000000000000000000000000000000000]
sage: ty = float
sage: numpy_dtype='double'
sage: numpy_array=numpy.array([ty(c) for c in
reversed(coeffs)],dtype=numpy_dtype)
sage: ext_rts1 = numpy.roots(numpy_array)
sage: ext_rts1
array([ 1.77245385, -1.77245385])
sage: rts = []
sage: for rt in ext_rts1:
....: rts.append(CDF(rt))
....:
sage: rts.sort()
sage: ext_rts = rts
sage: ext_rts
[-1.77245385091, 1.77245385091]
sage: rts = sorted([L(root.real()) for root in ext_rts if root.imag() ==
0])
sage: rts
[-1.7724538509055161039640324815991334617137908935546875000000,
1.7724538509055158819194275565678253769874572753906250000000]
}}}
which is the same as my final output, I think. Note that `ext_rts` still
have the same magnitude. This is a big-endian machine, I guess (PPC)? I
have no idea if that is relevant, and I note that the error seems to be
the opposite of the one others reported.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10042#comment:12>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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