Updates:
Status: Valid
Labels: Series
Comment #1 on issue 3298 by [email protected]: integrate / limit does not
know the sign of abs() / does nor catch NotImplementedError from limit()
http://code.google.com/p/sympy/issues/detail?id=3298
Nowadays, the error is:
In [5]: limit(integrate(abs(a)*exp(-abs(a)*x), x), x, oo)
---------------------------------------------------------------------------
NotImplementedError Traceback (most recent call last)
<ipython-input-5-bb74dd8ee8de> in <module>()
----> 1 limit(integrate(abs(a)*exp(-abs(a)*x), x), x, oo)
/home/asmeurer/Dropbox/sympy/sympy/series/limits.pyc in limit(e, z, z0, dir)
134 i, d = e.as_independent(z)
135 if i is not S.One and i.is_bounded:
--> 136 return i*limit(d, z, z0, dir)
137 else:
138 i, d = S.One, e
/home/asmeurer/Dropbox/sympy/sympy/series/limits.pyc in limit(e, z, z0, dir)
260
261 try:
--> 262 r = gruntz(e, z, z0, dir)
263 if r is S.NaN:
264 raise PoleError()
/home/asmeurer/Dropbox/sympy/sympy/series/gruntz.pyc in gruntz(e, z, z0,
dir)
676 r = None
677 if z0 == oo:
--> 678 r = limitinf(e, z)
679 elif z0 == -oo:
680 r = limitinf(e.subs(z, -z), z)
/home/asmeurer/Dropbox/sympy/sympy/core/cache.pyc in wrapper(*args,
**kw_args)
89 except KeyError:
90 pass
---> 91 func_cache_it_cache[k] = r = func(*args, **kw_args)
92 return r
93 return wrapper
/home/asmeurer/Dropbox/sympy/sympy/series/gruntz.pyc in limitinf(e, x)
470 e = e.subs(x, p)
471 x = p
--> 472 c0, e0 = mrv_leadterm(e, x)
473 sig = sign(e0, x)
474 if sig == 1:
/home/asmeurer/Dropbox/sympy/sympy/core/cache.pyc in wrapper(*args,
**kw_args)
89 except KeyError:
90 pass
---> 91 func_cache_it_cache[k] = r = func(*args, **kw_args)
92 return r
93 return wrapper
/home/asmeurer/Dropbox/sympy/sympy/series/gruntz.pyc in mrv_leadterm(e, x)
548 #
549 w = Dummy("w", real=True, positive=True, bounded=True)
--> 550 f, logw = rewrite(exps, Omega, x, w)
551 series = calculate_series(f, w, logx=logw)
552 series = series.subs(log(w), logw) # this should not be
necessary
/home/asmeurer/Dropbox/sympy/sympy/series/gruntz.pyc in rewrite(e, Omega,
x, wsym)
616 wsym = 1/wsym #if g goes to oo, substitute 1/w
617 elif sig != -1:
--> 618 raise NotImplementedError('Result depends on the sign
of %s' % sig)
619 #O2 is a list, which results by rewriting each item in Omega
using "w"
620 O2 = []
NotImplementedError: Result depends on the sign of -sign(Abs(a))
In other words, the catching of NotImplementedError in integrate() has been
fixed (and this uses the new algorithm anyway), but the Gruntz algorithm
ought to be able to compute the sign of -sign(Abs(a)). Perhaps the problem
is that a could be 0?
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