I'm attempting to write a formula that will determine a value of `a`

that minimizes the function output `myfun`

(i.e. `a-fptotal`

). MWE:

```
c <- as.matrix(c(.25,.5,.25))
d <- as.matrix(c(10000,12500,15000))
e <- 700
f <- 1.1
tr <- .30
myfun <- function(a) {
b <- max(a-e,0)
df <- data.frame(u1=c(c*b*.40),u2=c(c*b*.60))
df$year <- 1:nrow(df)
df$factor <- 1/(f)^df$year
df$d <- d
df$t <- (df$d-df$u1-df$u2)*tr
df$f <- df$d-df$t
df$fp <- df$f*df$factor
fptotal <- sum(df$fp)
return(a-fptotal) # what is a good approach to minimize this?
}
```

I've tried things like this without any success:

```
o2 <- optimize(myfun, lower = 0, upper = 30000)
```

The correct answer should be around `28355`

:

```
myfun(28355)
## [1] -1.04151
```

Any thoughts are appreciated. Thank you!