[R] find max. value for a equation by optimize

[Jianling Fan]

Hello, everyone,

I have a specific equation, When I draw it out, I found there is a
max. value for it at about x=5. but I couldn't point it out by
optimize(). Does anyone know why? Thanks!

my code is:

d50<-18.04
c<-  -1.276
dm<-147

sm <- function (x) {
  1/(1+(x/d50)^c)+(1-1/(1+(dm/d50)^c))*x/dm-(1/(1+((x-1)/d50)^c)+(1-1/(1+(dm/d50)^c))*(x-1)/dm)
}
curve(sm, 0,50)
optimize(sm,c(0,50))

The optimize() only give min. value but not max.