Re: Result from FindRoot

```Torbjörn Randahl wrote:

> How do I use the result from FindRoot in a Plot?
>
> The resullt from FindRoot is like:
> Out[4]:¿-> 300 000}
>  how do I assign the result directly to a variable  or  how do I set the
> variable f to the
> resulting (root)?
>
> i.e I want to change another variable in the expression and then Plot
> the root!

Tobbe:

Plotting:

In[1]:Plot[x/.FindRoot[Tan[x]Ðf, {x,f}], {f,0,Pi/2.1}, PlotRange -> All]

On assinging to variables:

In[2]:FindRoot[Sin[x]Ð0, {x,3}]

Out[2]{x -> 3.14159}

In[3]:newvar /.%

Out[3]3.14159

In[4]:newvar

Out[4]3.14159

More directly

In[5]:newvar2 /.FindRoot[Sin[x]Ð0, {x,3}];

In[6]:newvar2

Out[6]3.14159

We can define a function of parameters

In[7]:root[a_,b_]  :. FindRoot[Sin[x -b]Ð0, {x,a}]

and a version that remembers the answers

In[8]:root2[a_,b_]  :¸ot2[a,b] . FindRoot[Sin[x -b]Ð0, {x,a}]

In[9]:root2[ 1,4]

Out[9]0.858407

In[10]:?root2

From In[10]:Global`root2
root2[1, 4] .8584073466995231

root2[a_, b_] :
root2[a, b]  /. FindRoot[Sin[x - b] Ð0, {x, a}] --

Allan Hayes
Mathematica Training and Consulting
Leicester, UK
hay@haystack.demon.co.uk
http://www.haystack.demon.co.uk
voice: +44 (0)116 271 4198
fax: +44 (0)116 271 8642

```

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