Re: Help! FindRoot output to list...

• To: mathgroup at smc.vnet.net
• Subject: [mg30981] Re: [mg30958] Help! FindRoot output to list...
• From: Tomas Garza <tgarza01 at prodigy.net.mx>
• Date: Sat, 29 Sep 2001 04:19:00 -0400 (EDT)
• References: <200109280755.DAA01716@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Since you already mention that the output is a list, you're close to the
solution. It is very important that you grasp what's going on. Example:

In[1]:=
r = FindRoot[x - 4 == 0, {x, 0}]
Out[1]=
{x -> 4.}
In[2]:=
FullForm[r]
Out[2]//FullForm=
List[Rule[x, 4.`]]

Here you see that the result is indeed a list *with only one element*. This
element you extract with

In[3]:=
r[[1]]
Out[3]=
x->4.

and then, the value you want is
In[4]:=
r[[1,2]]
Out[4]=
4.

But you may also use a ReplaceAll command to directly have the root
available:

In[5]:=
x/.r
Out[5]=
4.

or even more directly

In[6]:=
x/.FindRoot[x - 4 == 0, {x, 0}]
Out[6]=
4.

Tomas Garza
Mexico City

----- Original Message -----
From: "Joachim Almergren" <joal at sissa.it>
To: mathgroup at smc.vnet.net
Subject: [mg30981] [mg30958] Help! FindRoot output to list...

>
> I would be extremely thankful to anyone
> who can provide me with a solution for
> converting the FindRoot output list to
> a list of the 'usable' numbers.
> (With other word getting rid of the "x->"
>  part of the list.)
>