#2371 limit((exp(a*x)-1)/(exp(a*x)+1),x,inf) fails

None
closed
Dan Gildea
5
2014-10-08
2012-03-16
Raymond Toy
No

Maxima is unable to compute the limit of (exp(a*x)-1)/(exp(a*x)+1) as x -> inf. Maxima asks if a is positive or negative or zero. If you answer positive or negative, it returns the noun form. Perversely if you answer zero, the limit is -1. But if a is zero, the expression is exactly 0.

If a number is substituted for a, then maxima correctly returns 1 or -1 depending on the sign of a.

Discussion

  • Dan Gildea
    Dan Gildea
    2014-10-08

    • status: open --> closed
    • assigned_to: Dan Gildea
    • Group: --> None
     
  • Dan Gildea
    Dan Gildea
    2014-10-08

    Fixed by [100120a026260fea89a8007667e70f6cccb072d2]

    src/limit.lisp:
    o ratlim: give up rather than returning '$infinity when
      sign in unknown.
    
    Not sure how to add a test case for this, since it involves
    interaction with the user.
    
     

    Related

    Commit: [100120]