# [R] basic math question?

Uwe Ligges ligges at statistik.uni-dortmund.de
Sun May 20 22:53:08 CEST 2007

```AP05 wrote:
> This seems like it's easy but I can't seem to get it.
>
>
> My equation is (a^b)/c = d.
>
> I know that I can solve for b via
>
> log(d*c) / log(a) = b
>
>
> However, I don't really have d in the first place I have d/sum(d)
> values...no d's...just d/sum(d) values that all add to 1.0
>
> So, for example, if my data is
>
> a=4,9,12,3
> b=unknown
> c=12,18,13,20
> d/sum(d)=43,45,23,18

d/sum(d) should indeed add to one, hence I do not understand the data
above...

If you do not have d (but only d/sum(d)), then you simply cannot
estimate b in (a^b)/c = d. At least, the solution is not unique.

BTW: In what sense is this related to R(-help)?

Uwe Ligges

>
> I need an estimate of b. How can I do model and code this?
>
> Again, b is a power term of a and b^a are divided by c.
>
> Thank you,
> Jeff
>
>
>
>
> Checked by AVG Free Edition.
>
> PM
>
>
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