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Re: error message

  • To: mathgroup at
  • Subject: [mg5083] Re: error message
  • From: rubin at (Paul A. Rubin)
  • Date: Fri, 25 Oct 1996 22:48:42 -0400
  • Organization: Michigan State University
  • Sender: owner-wri-mathgroup at

In article <54kal9$d6r at>,
   gt1824a at (Heather Mary Hauser) wrote:
->In using FindRoot to find the zeros of a function which I have defined by 
->procedure (too long to list here), I keep getting the error message 
->"FindRoot::frnum:Function{{-0.00004794 - 0.000020387I}} is not a length 1
->list of numbers at {r} = {0.15I}" . r = 0.15I is the first of two values 
->give to start the search, because I know that there is not a symbolic 
->derivative to be found. I also know that this value is near a possible 
->because it is midway through an interval where the function changes sign. 
->(both real and imaginary parts). Can anybody tell me what this error 
->means ?
->Heather Hauser
->heather at

I can't be 100% certain without seeing the procedure code, but I think the 
problem is the nested set braces.  FindRoot is substituting .15 I for r in 
the function definition and expecting to get back a list containing one 
number.  (I *think* FindRoot does the substitution using replacement, which 
means the function is expected to spit back a number, and replacement 
presents it as a list consisting of that number.)  The function, however, 
is apparently returning a *list* {-0.00004794 - 0.000020387I}, which the 
replacement operations surrounds with another pair of braces, thus yielding 
a list whose sole entry is a list (containing one number).  Check your proc 
and see if it isn't making a list out of the answer.

-- Paul

* Paul A. Rubin                                  Phone: (517) 432-3509   *
* Department of Management                       Fax:   (517) 432-1111   *
* Eli Broad Graduate School of Management        Net:   RUBIN at MSU.EDU    *
* Michigan State University                                              *
* East Lansing, MI  48824-1122  (USA)                                    *
Mathematicians are like Frenchmen:  whenever you say something to them,
they translate it into their own language, and at once it is something
entirely different.                                    J. W. v. GOETHE

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