# [R] Excel can do what R can't?????

Roger D. Peng rpeng at stat.ucla.edu
Thu Jul 17 07:42:32 CEST 2003

```I'm having a little difficulty understanding this thread.  If Excel can
do the job correctly and suits your needs, why not just use Excel?

As far as I know, 'optim' cannot optimize a function subject to
arbitrary equality constraints.  The 'constrOptim' function allows for
linear inequality constraints but in general, you will either have to
function.  Also, just a small note, but using lexical scoping in your
problem would eliminate the need to have all those variables defined in
the global environment (but otherwise it won't change anything).

-roger

Michael Rennie wrote:

>Hi, Reid and Spencer-
>
>I think I've figured something out pretty critical to the problem.
>
>Loking at my 'solver' options, I have a condition added that 'Hgtmod = Hgt'.
>Without this conditional statement, I have to run solver 3-4 times before I get
>a final solution. MEANING- solver and R, when left to their own devices, suck
>equally at finding a solution with similar starting points.  BUT, given a
>conditional statement that demands Hgt = Hgtmod, it gives it somewhere to look
>withing the given parameter space.
>
>So, the millon dollar quesiton: Is there any way of setting up a contitional
>statement like this in 'optim', to specify a solution such that Hgtmod = Hgt?
>Or, write it into function f?  The control statements 'fnscale' and 'parscale'
>

I don't think 'fnscale' or 'parscale' will help you here at all.  If you
want a constraint you need to specify it in the objective function
directly (something like an additive penalty).

>look like candidates, but will only help me if I build Hgtmod into the
>optimization statement- can I do that?  How do you specify multiple
>parameters?  Or should I specify two functions to optimize- one, fucntion f,
>and a second, something like
>
>g<- (Hgt = Hgtmod)^2
>
>Can I do that? If this is all I need to do, I am off to the races, and owe you
>both a beer!  I'm going to try some stuff. All is not lost! If you have any
>ideas, I'd love to hear them.
>
>THanks again for everything.....
>
>
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>

```