Re: FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg31512] Re: FindRoot
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Thu, 8 Nov 2001 04:55:50 -0500 (EST)
- References: <9sb3u5$8oc$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
<Pieter-Jan.DeSmet at fys.kuleuven.ac.be> wrote in message news:9sb3u5$8oc$1 at smc.vnet.net... > Dear Sir, > > Can you clarify the following error message? > > In[3]:= f[i_] := x == i > > In[5]:= FindRoot[f[1], {x, 0}] > > FindRoot::frnum: Function {False} is not a length 1 list of > numbers at {x} = {0.}. > > Out[5]=FindRoot[f[1], {x, 0}] > > > This is a simplified version of an error message I got in a more > difficult case. I hope that I have not made a stupid mistake. > > Thank you very much > > Pieter-Jan De Smet > Pieter: FindRoot[Evaluate[f[1]],{x,0}] {x->1.} The reason is that FindRoot has the attribute HoldAll, and unevaluated f[1] is an improper entry. -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565