#630 limit(erf(n*x),n,inf) depends on n (x=0)

closed
nobody
None
5
2004-11-20
2004-10-22
No

assume(equal(zz,0))$

limit(erf(n*zz),n,inf) => erf(n*zz)

A limit result should be independent of the dummy
variable! -- in this case result is 0.

For other functions, limit gets this right:

makelist( limit(f(zz*x),x,inf) ,
f, [sin,exp,gamma,atan,erf] )

=> [0, 1, 1, 0, ERF(x zz)]

Limit/erf works correctly for zz>0 and zz<0.

Discussion

  • Raymond Toy

    Raymond Toy - 2004-11-19

    Logged In: YES
    user_id=28849

    This is caused by simplim%erf-%tanh taking the default
    branch and returning:

    (simplify (list (ncons fn) arg))

    I think that "arg" should really be "arglim", because the
    arg has the known limit arglim, and erf (and tanh) don't
    have singularities anywhere to worry about.

     
  • Raymond Toy

    Raymond Toy - 2004-11-20

    Logged In: YES
    user_id=28849

    Fix applied.

     
  • Raymond Toy

    Raymond Toy - 2004-11-20
    • status: open --> closed
     

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