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'Double' FindRoot

• To: mathgroup at smc.vnet.net
• Subject: [mg8690] 'Double' FindRoot
• From: Michaela Meier <michaela.j.meier at rz.ruhr-uni-bochum.de>
• Date: Mon, 15 Sep 1997 02:49:16 -0400
• Organization: Ruhr-Uni-Bochum
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

I've got another serious problem

I'm trying to find a numerical solution to a set of three equations:

1)

FindRoot[
  {fa[0.1,x1]==fa[x2,x3],
   fb[0.1,x1]==fb[x2,x3],
   fc[0.1,x1]==fc[x2,x3]},
  {x1,0.1},{x2,0.1},{x3,0.9}]

Worst of all: fa, fb, and fc are defined as:

(this is a simplified example !)

2)

fa=Function[{y1,y2},
      fr=FindRoot[
           {a1 x + b1 y + c1 z == p1[y1,y2],
            a2 x + b2 y + c2 z == p2[y1,y2],
            a3 x + b3 y + c3 z == p3[y1,y2]},
            {x,0.1},{y,0.1},{z,0.1}];
      
            x + y + z /. fr
   ]

Just typing 'fa[1,2]' produces NO error.

But as soon as I start program 1) Mathematica says that it's expecting a
'list of length 3'
Again: If I calculate 'fa' all by itself it returns a number for all
combinations of y1 and y2

So what causes this error ?? Or  isn't  Mathematica able to do more than
one FindRoot at the same time ????


Michaela