[R] help with optimize statement

From: tom wright <tom_at_maladmin.com>
Date: Sat 25 Feb 2006 - 00:43:07 EST


Can some help me spot what I'm doing wrong here. I have two equations, one a michalis-menton eqn and one a straight line. I need to work out where they cross.

I created the function:
solveEqn<-function(x,vals){
Vmax<-vals[1]
Ks<-vals[2]
m<-vals[3]
c<-vals[4]

    diff<-0
    mmVal<-exp(Vmax+x/(Ks+x))
    slVal<-x*m+c

    diff<-mmVal-slVal
    return(diff)
}
> optim(c(200,500),solveEqn,vals=c(2.4591201,-0.4015233,5.924e-5,3.437))
Error in optim(c(200, 500), solveEqn, vals = c(2.4591201, -0.4015233, :

        objective function in optim evaluates to length 2 not 1

If i replace return(diff) with sum(diff) then the optim function runs but returns the wrong value (which should be about 290).

Many thanks
Tom



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