Status: Accepted
Owner: [email protected]
Labels: Type-Defect Priority-Critical Milestone-Release0.7.0
New issue 2151 by [email protected]: BasicMeta.keep_sign
http://code.google.com/p/sympy/issues/detail?id=2151
After discussions in issue 1587, it seems that the consensus is that
BasicMeta.keep_sign should be set to True and that this switch should then
be removed.
So the first step is to get all the tests to run with keep_sign set to
true. I get 3 failures with bin/test under Python 2.6.6. Two of them are
obvious and direct consequences of the setting:
assert -1/(-1-x) == 1/(1+x)
assert (3-y)**2 == (y-3)**2
The third one is a real bug:
______ sympy/concrete/tests/test_sums_products.py:test_evalf_slow_series
_______
File "/media/sda2/Boulot/Projets/sympy-git/sympy/concrete/tests/test_sums_products.py",
line 90, in test_evalf_slow_series
assert NS(Sum((-1)**n / n, (n, 1, oo)), 15) == NS(-log(2), 15)
File "/media/sda2/Boulot/Projets/sympy-git/sympy/concrete/tests/test_sums_products.py",
line 53, in NS
return str(sympify(e).evalf(n, **options))
File "/media/sda2/Boulot/Projets/sympy-git/sympy/core/evalf.py", line
1040, in evalf
result = evalf(self, prec+4, options)
File "/media/sda2/Boulot/Projets/sympy-git/sympy/core/evalf.py", line
972, in evalf
r = rf(x, prec, options)
File "/media/sda2/Boulot/Projets/sympy-git/sympy/core/evalf.py", line
880, in evalf_sum
v = hypsum(func, n, int(a), prec2)
File "/media/sda2/Boulot/Projets/sympy-git/sympy/core/evalf.py", line
844, in hypsum
raise ValueError("Sum diverges like n^%i" % (-p))
ValueError: Sum diverges like n^3
I've tracked it down to sympy.core.evalf.hypsum():
In [8]: hypsum((-1)**n / n, n, 1, 25)
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/media/sda2/Boulot/Projets/sympy-git/<ipython console> in <module>()
/media/sda2/Boulot/Projets/sympy-git/sympy/core/evalf.pyc in hypsum(expr,
n, start, prec)
842 raise ValueError("Sum diverges like (%i)^n" % abs(1/g))
843 if p < 1 or (p == 1 and not alt):
--> 844 raise ValueError("Sum diverges like n^%i" % (-p))
845 # We have polynomial convergence: use Richardson
extrapolation
846 # Need to use at least quad precision because a lot of
cancellation
ValueError: Sum diverges like n^3
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