[R] How to solve difficult equations?

[Robert A LaBudde]

At 03:15 AM 4/25/2007, francogrex wrote:

>This below is not solvable with uniroot to find "a":
>fn=function(a){
>b=(0.7/a)-a
>(1/(a+b+1))-0.0025
>}
>uniroot(fn,c(-500,500))  gives
>"Error in uniroot(fn, c(-500, 500)) : f() values at end points not of
>opposite sign"
>
>I read R-help posts and someone wrote a function:
>http://finzi.psych.upenn.edu/R/Rhelp02a/archive/92407.html
>but it is not very precise. Is there any '"standard" function in R that can
>solve this? thanks.

Actually, if you're solving fn(a)==0, then some trivial algebra leads 
to a linear equation with a=0.001754.

Why are you trying to solve this numerically? Is it a single instance 
of a larger, more general problem?

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Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
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