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Re: fsolve features

From: Francesco Potorti`
Subject: Re: fsolve features
Date: Mon, 5 Jul 1999 15:58:29 +0200 (CEST)

   >> [x,RC]= fsolve(f='x^2 +1',randn(1)); #>V2.0.14
    >>      #NOTE: prior to V2.0.14 , you have to  define  f  explicitely:
    >>      #function y=f(x) y=x^2+1; end
    >>      #[x,RC]=fsolve('f',randn(1))
   > !!!  Where is this documented?
   In octave V2.0.14 documentation  (

...  I looked for it and didn't find it.  Which node?
   >>   (2)   a call to fsolve  like :  [x,info]=fsolve('f',x0)   is adequate 
   >>  function   (vector) Y =  f ( vector X  ) 
   >>        >>> where Y and X have same length <<<<
   >>         It's supposed to handle equally sized problems only!
   >>   It is easy to work around this. 
   >>   Maybe you are suggesting that a workaround
   >>   is nt what you would like to have?
   If this's SO EASY why didn't/don't YOU hack these obviously rather
   limited couple of short program lines together and provide it to the
   public ?  Why didn' anybody else do such an EASY job within the last 5
   years or so ...?

...  Feeling aggressive?

I mean that in practice, as far as I can see, if you have X=f(Y), then:
- if X=[x1,x2,x3], Y=[y1,y2], then you can change it by specifying
  Y=[y1,y2,0], and making f ignore the third element of Y
- if X=[x1,x2], Y=[y1,y2,y3], then you can make f return [x1,x2,0]

This is a simple workaround that  needs no coding in practically all cases.
Yes, it's not elegant (that's why  I'm calling it a workaround), and it may
not be straightforward, so everyone would like a better solution.

I  may be obviously  missing something,  and in  this case  I'd like  to be
addressed in the right direction.
   Looking back at more than one year's intense ( homebrew ... not full )
   work dealing with this problem while reading your statement above, I get
   in really great doubt, whether my conceptual approach to the problem
   could be smart enough to be efficient in contrast to your genious EASY
   solution !

Yes, you feel aggressive.

As far  as I  understand, your  work deals with  much deeper  problems than
making  fsolve manage  differently sized  vectors.   Why do  you insist  on
trying to bash me on unimportant details?
   Obviously, there seems to be no necessity anymore to finish this project
   from my side ....
I am sorry  that you feel this  way, and if you reread  my previous answers
you may be able to see that  there was no offense in them.  Certainly there
was no offense intended.

On the other  hand, if you choose to feeling  offended nonetheless, I'd say
that you  should value your work  and its usefulness to  the general public
much more than some random comments you receive on a public mailing list.

Francesco Potortì (researcher)         Voice:    +39-050-593 203 (op. 211)
Computer Networks Group                Fax:      +39-050-904052
CNUCE-CNR, Via Santa Maria 36          Email:    address@hidden
56126 Pisa - Italy                     Web:

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