# Re: Eureqa - Re: Formulize - Sum of the Variables divided by the Number of Variables

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### aid...@cox.net

Jul 24, 2013, 2:54:11 AM7/24/13
Yes your interpretation of what I was trying to do was correct
And the formula looks good.
Thank you again Alison
Nevi

---- Alison Reynolds <alison....@nutonian.com> wrote:
> Hi Nevi,
>
> First let me clarify exactly what you are looking for. Is the idea that
> given variable x1, x2, ... x8, you want the model produced to look like:
>
> z = (x1 + x2) / 2
> or
> z = (x1 + x2 + x3) / 3
>
> where the variables could be any subset of the 8 variables, and the
> denominator will be the number of variables? I.e. you expect that z will
> be the mean of some subset of the input variables?
>
> If my understanding is correct, then I think you can use a target
> expression that looks like this:
>
> y = (step(f0())*x1 + step(f1())*x2 + step(f2())*x3)/(step(f0()) +
> step(f1()) + step(f2()))
>
> (Mine is set up for 3 input variables; you'll need to update it for 8).
> The expressions step(fn()) will map to either 0 or 1. On the numerator
> that will either include or exclude a variable from being included in the
> sum of variables. On the denominator it will contribute to the count of
> variables. I've attached a sample project that shows that expression used
> in 2 searches. The solutions produced (once Eureqa has simplified them)
> are:
>
> y = 0.5*x1 + 0.5*x2
> and
> y = 0.3333*x1 + 0.3333*x2 + 0.3333*x3
>
> Those of course can be rewritten in the format you are looking for..
>
> y = (x1 + x2) / 2
> and
> y = (x1 + x2 + x3) / 3
>
> Let me know if that's what you were looking for.
> Alison
>
>
> On Mon, Jul 22, 2013 at 12:59 AM, aidabet <aid...@cox.net> wrote:
>
> > Another question
> >
> > Example Target Expression
> >
> > z = f(x1, x2, x3, x4, x5, x6, x7, x8)
> >
> > ****
> >
> > I’m looking for a way to Sum the number of variables being considered for
> > a Solution and divide the Sum of the Variables by the Number of Variables,
> > all included in the Final Solution.
> >
> > ****
> >
> > So the Final Solution would resemble
> >
> > z = f(( x1 + x2 ) / 2 ) if two variables used
> >
> > z = f(( x1 + x2 + x3 ) / 3 ) if three variables used
> >
> > ****
> >
> > If it’s possible your help is appreciated
> > Thanks
> >
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