[R] Plotting several functions in the same display (again)
Duncan Murdoch
murdoch.duncan at gmail.com
Thu Apr 4 19:07:02 CEST 2013
On 04/04/2013 11:38 AM, Julio Sergio wrote:
> To superimpose two functions plots in the same page. The functions L0
> and L1, as defined below, I use the following code:
>
> # An accumulative normal distribution function with
> # several parametres
> f0 <- function(mu, xm, ds, n) {
> 1 - pnorm((xm-mu)/(ds/sqrt(n)))
> }
>
> f1 <- function(mu,n) f0(mu, 386.8, 48, n)
>
> # Two functions with just the parameter mu
> L0 <- function(mu) f1(mu, 36)
> L1 <- function(mu) f1(mu,100)
> plot(L0,ylim=c(0,1),xlim=c(360,420))
> curve(L1,add=T)
>
> However, I'm puzzled with a problem in the same line: When I passed a
> "function producer" to plot, again it worked well; however it didn't work in
> the same way when trying to use this same argument in curve. See what I'm
> talking about:
>
> # A particular normal distribution function:
> dn8 <- function(z,m) dnorm(z,m,8) # norm dist with sd=8
>
> # A function that produces functions:
> # returns a function such that given a mean(i) depends only
> # on z
> fi <- function(i) function(z) dn8(z,i)
>
> plot(fi(370),xlim=c(360,420)) # Works well!
>
> curve(fi(380),add=T) # This doesn't work
>
> # However, if I put it in this way, surprisingly, it works!
> ff <- fi(380)
> curve(ff,add=T)
>
> I cannot understand this behaviour. Could anyone give me some feedback on
> this?
The curve() function is trying to be clever, but it's not. You can
probably get what you want using curve(fi(380)(x), add=TRUE). It treats
the "x" argument specially.
Duncan Murdoch
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