R help - Jun 2007 - Iterative Solver [Converting Matlab's solve()]

I can't for the life of me figure out how to get the roots for this simple
(but sovable only iteratively) equation in R:

x = z*(1-(1-2/z)^y

where x and y are known, and z is unknown. In Matlab, this amounts to:

[my.solution] = solve('x = z*(1-(1-2/z)^y') 
my.solution.real = solution(y-1,y)

% bottom line displays non-imaginary solution (last element)

Obviously, I'm deeply unqualified as a mathematician or programmer and 
regret wasting your time if this question is really basic. I would very 
much appreciate even the smallest morsel of time that you might spend on 
this, and yes, you could be my hero.

Many Thanks,

Boris

P.S. The above equation is from: Paxman GJ (1963). Maximum likelihood 
estimation of the number of self-sterility alleles in a population. 
Genetics 48: 1029-1032.

At 12:24 AM 6/19/2007, Boris wrote:
>I can't for the life of me figure out how to get the roots for this
simple
>(but sovable only iteratively) equation in R:
>
>x = z*(1-(1-2/z)^y
>
>where x and y are known, and z is unknown. In Matlab, this amounts to:
>
>[my.solution] = solve('x = z*(1-(1-2/z)^y')
>my.solution.real = solution(y-1,y)
>
>% bottom line displays non-imaginary solution (last element)
><snip>
1.  Your equation is syntactically incorrect. It is missing a ")". 
Ditto for your Matlab example.

2. Are you looking for an analytical (symbolic) solution? If so, I 
don't believe one exists (if you place a ")" after y).

3. To find numerical roots, see uniroot().

4. If you want more help, you'll have to specify domains or values for x and
y.

===============================================================Robert A.
LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
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