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fzero documentation

From: Bart Vandewoestyne
Subject: fzero documentation
Date: Mon, 29 Nov 2010 11:56:04 +0100
User-agent: Mutt/1.5.20 (2009-06-14)

Hello all,

Today, while preparing a lab session for my students, I was playing around with
fzero and I noticed some inconsistencies in the documentation.  I'm not sure if
this is the place to report them and if these are fixed in later releases of
Octave... Feel free to forward my mail to the appropriate place.

My comments concern Octave 3.2.4 on Ubuntu 10.10 (installed using the packaging

1) the OUTPUT output argument of fzero is not documented.

2) the help of fzero mentions 'x0 specifies a starting point'.  Trying with the
equation x+log(x)=0 (solution is 0.56714) gives me:

  octave:3> fzero(@(x) x+log(x), 0.5)
  ans =  0.56714

  octave:4> fzero(@(x) x+log(x), 0.9)
  error: fzero: zero point is not bracketed
  error: called from:
  error:   /usr/share/octave/3.2.4/m/optimization/fzero.m at line
  255, column 1

  octave:4> fzero(@(x) x+log(x), [0 1])
  ans =  0.56714

so in certain situations a single starting point works, but in other situations
this doesn't work and one has to specify a starting interval.  This is not
clear from the help...

3) The help of fzero refers to the optimset command for a description of
certain options that one can specify.  However, `help optimset' does not show
me any info regarding these options.  All I get is:

  octave:5> help optimset
  `optimset' is a function from the file 
   -- Function File:  optimset ()
   -- Function File:  optimset (PAR, VAL, ...)
   -- Function File:  optimset (OLD, PAR, VAL, ...)
   -- Function File:  optimset (OLD, NEW)
       Create options struct for optimization functions.
  Additional help for built-in functions and operators is
  available in the on-line version of the manual.  Use the command
  `doc <topic>' to search the manual index.
  Help and information about Octave is also available on the WWW
  at and via the address@hidden
  mailing list.

Kind regards,

        "Share what you know.  Learn what you don't."

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