Not getting correct limits

[div...@umich.edu]

The following code was run using sympy version 1.0, python version 3.4, Anaconda installation.

import sympy as spy
import sympy.abc as abc


N, k = spy.symbols('N, k', positive = True)
es = 1 - (1 - 1/(2*N))**k
e = 2*N*es
spy.pprint(e)
c0 = spy.limit(e, N, spy.oo)
spy.pprint(c0)
c1 = spy.limit(N*(e-c0), N, spy.oo)
spy.pprint(c1)
c2 = spy.limit((e-c0-c1/N)*(N*N), N, spy.oo)
spy.pprint(c2)
c2x = spy.limit(e*N*N-c0*N*N-c1*N, N, spy.oo)
spy.pprint(c2x)

It prints

 

    ⎛           k    ⎞
    ⎜  ⎛     1 ⎞     ⎟
2⋅N⋅⎜- ⎜1 - ───⎟  + 1⎟
    ⎝  ⎝    2⋅N⎠     ⎠
k
   2    
  k    k
- ── + ─
  4    4
-∞
 3    2    
k    k    k
── - ── + ──
24   8    12

As you can see, the result for c2 is wrong, although it is able to calculate c2x correctly. 

Can someone please clarify what is going on?

Thanks!

[Aaron Meurer]

This looks like a bug. Can you open an issue for it?

Aaron Meurer

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[div...@umich.edu]

Sure I will. The bug is still present  in version 1.1.1 of sympy (Python 3.6).