FindRoot question (number of variables)

*To*: mathgroup at smc.vnet.net*Subject*: [mg15743] FindRoot question (number of variables)*From*: "Doug Webb" <D_Webb at prodigy.net>*Date*: Fri, 5 Feb 1999 03:42:38 -0500 (EST)*Organization*: Prodigy Services Corp*Sender*: owner-wri-mathgroup at wolfram.com

Hello, This is a simplified example of I problem I have run into with FindRoot. Does anybody have any idea why it's doing what it is? And if so, how I can make it do what I want, or some other work around? Thanks for any info. Here's the example: define a function that takes one input, and outputs two results: r[x_] := {x, x^2} It does what's expected: r[4] {4,16} Now, find a solution using FindRoot: FindRoot[ r[x] == {5, 25}, {x, 2}] returns an error (rather than the obvious answer of x->5): FindRoot::"frnum": "Function {{-3., -21.}} is not a length 1 list of numbers at {x} = {2.}." It seems that FindRoot REQUIRES you to solve for as many variables as your function returns. Even though when entered seperatly, r[5] == {5, 25} returns "true". Why? Any ideas? Or any ideas how to get around this "feature" of FindRoot? Thanks for any input. Doug D_Webb at prodigy.net Douglas.S.Webb at maf.nasa.gov

**Follow-Ups**:**Re: FindRoot question (number of variables)***From:*Daniel Lichtblau <danl>