Status: Accepted
Owner: asmeurer
Labels: Type-Defect Priority-Medium Series
New issue 2670 by asmeurer: In [65]: a Out[65]: ⎛
2⎞ r⋅cos(θ) + ⅈ⋅r⋅sin(θ) + O⎝r ⎠ In [66]: limit(a/(r*(cos(theta) +
I*sin(theta))), r, 0) Out[66]: O(1)
http://code.google.com/p/sympy/issues/detail?id=2670
In [65]: a
Out[65]:
⎛ 2⎞
r⋅cos(θ) + ⅈ⋅r⋅sin(θ) + O⎝r ⎠
In [66]: limit(a/(r*(cos(theta) + I*sin(theta))), r, 0)
Out[66]: O(1)
r and theta are real. The answer should be 1. You get this is you expand
the result first.
In [74]: limit(expand(a/(r*(cos(theta) + I*sin(theta)))), r, 0).simplify()
Out[74]: 1
Also, a similar limit doesn't work at all unless it is expanded
In [75]: limit((x + O(x**2))/x, x, 0)
---------------------------------------------------------------------------
NotImplementedError Traceback (most recent call last)
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/<ipython-input-75-627d8140a49e>
in
<module>()
----> 1 limit((x + O(x**2))/x, x, 0)
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/series/limits.pyc
in
limit(e, z, z0, dir)
190
191 try:
--> 192 r = gruntz(e, z, z0, dir)
193 if r is S.NaN:
194 raise PoleError()
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/series/gruntz.pyc
in
gruntz(e, z, z0, dir)
686 else:
687 raise NotImplementedError("dir must be '+' or '-'")
--> 688 r = limitinf(e0, z)
689
690 # This is a bit of a heuristic for nice results... we always
rewrite
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/core/cache.pyc
in
wrapper(*args, **kw_args)
99 except KeyError:
100 pass
--> 101 func_cache_it_cache[k] = r = func(*args, **kw_args)
102 return r
103 return wrapper
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/series/gruntz.pyc
in
limitinf(e, x)
478 e = e.subs(x, p)
479 x = p
--> 480 c0, e0 = mrv_leadterm(e, x)
481 sig = sign(e0, x)
482 if sig == 1:
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/core/cache.pyc
in
wrapper(*args, **kw_args)
99 except KeyError:
100 pass
--> 101 func_cache_it_cache[k] = r = func(*args, **kw_args)
102 return r
103 return wrapper
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/series/gruntz.pyc
in
mrv_leadterm(e, x)
536 return (e, S.Zero)
537 if Omega == SubsSet():
--> 538 Omega, exps = mrv(e, x)
539 if not Omega:
540 # e really does not depend on x after simplification
/Users/aaronmeurer/Documents/python/sympy/sympy-scratch/sympy/series/gruntz.pyc
in
mrv(e, x)
365 " not implemented yet.")
366 return mrv(e.args[0], x)
--> 367 raise NotImplementedError("Don't know how to calculate the mrv
of '%s'" % e)
368
369 def mrv_max3(f, expsf, g, expsg, union, expsboth, x):
NotImplementedError: Don't know how to calculate the mrv of 'O(1/_p)'
In [76]: limit(expand((x + O(x**2))/x), x, 0)
I'm not sure if I should mark this is WrongResult. Is O(1) wrong? I think
it's technically correct, but of course not what we want.
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