Re: ?
- To: mathgroup at smc.vnet.net
- Subject: [mg120809] Re: ?
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Thu, 11 Aug 2011 05:12:08 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
On 8/10/11 at 6:47 AM, david.kirkby at onetel.net (David Kirkby) wrote:
>The output of FindRoot[] when trying to find a root is like:
>{x -> 0.49454545}
>How can I convert that list, into the number 0.49454545?
>In[1]:= FindRoot[x+9,{x,-5}]
>Out[1]= {x -> -9.}
>In[2]:= Head[%]
>Out[2]= List
>I can't seem to find any "normal" operations on the list which give
>me the number.
The output from FindRoot is a list of replacement rules. When
there is a single replacement rule simply do
In[1]:= sol = FindRoot[x + 9, {x, -5}];
In[2]:= x /. sol
Out[2]= -9.
When there is more than one replacement rule you will need to
specify which solution you want. For example using Solve
In[3]:= sol = Solve[x^2 == 9, x];
In[4]:= x /. sol[[1]]
Out[4]= -3
In[5]:= x /. sol[[2]]
Out[5]= 3