Hello,
>
> Hi Emily,
>
> Yes (see below), but you might be better off by writing a simple
> function. Here are examples both ways (usually eval parse is highly
> discouraged).
>
> Cheers,
>
> Josh
>
Yes, eval/parse is discouraged but there's a way of using it,
that is less troublesome, to create a function.
(Maybe Emily was thinking of symbolic mathematics software - my personal
favorite is
Maple but there is also open source Maxima)
makefun <- function(text){
x <- numeric()
function(x) eval(parse(text=text))
}
txt <- 'x^2 + x + 5'
g <- makefun(txt)
g(6)
g(c(6, 5, 3, 10, 20))
(opt <- optimize(g, interval=c(-300, 300)))
curve(g, from=-5, to=5)
points(opt$minimum, opt$objective, col='red')
This may be usefull if you don't know the function's analytic expression
beforehand.
Hope this helps,
Rui Barradas
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