# [R] trying to plot function using curve

Faheem Mitha faheem at email.unc.edu
Wed Apr 16 04:50:43 CEST 2003

```Dear People,

I hope someone can help me with this. I have a function (density) which I
am trying to plot using curve. I am calling mg.hist(3,2,1), and getting
the following errors.

Error in xy.coords(x, y, xlabel, ylabel, log) :
x and y lengths differ
In addition: There were 50 or more warnings (use warnings() to see the
first 50)
> warnings()
1: longer object length
is not a multiple of shorter object length in: x * y

and more of the same.

I'm not sure where the problem is. I assume it has something to do with me
incorrectly vectorising my functions(s). However, it seems to me that
density() is vectorised.

By the way, if anyone would like to suggest a better way to plot density
plots, please let me know. curve() was suggested to me, which is why I am
using it. Actually, I want to plot a density curve on top of a histogram.
I was thinking of trying to use trellis graphics for this, but I'm not
sure it has any advantages for this purpose.

Faheem.

***********************************************************************

mg.hist <- function(len,theta,pos)
{
postscript(file="plot.ps", horizontal = FALSE, onefile = FALSE, paper
= "special", width=6, height=4)

densityfn <- function(x)
{
density(x,theta,pos,len)
}
curve(densityfn)
dev.off()
}

density <- function(x,theta,pos,len)
{
if((len !=2) && (len !=3))
stop("length must be 2 or 3")
if((pos < 1) || (pos > len))
stop("pos must be between 0 and len-1")

if(len==2)
{
if((pos==1) || (pos==2) )
{
unnorm <- function(x)
{
ifelse(x==0,2*theta,(exp(theta*x)-exp(-theta*x))/x)
}
return(unnorm(x)/
integrate(unnorm,lower = -theta, upper = theta,
subdivisions=1000)\$value)
}

}

if(len==3)
{
if((pos==1) || (pos==3))
{
unnorm1 <- function(y) ##here y is 2-dim
{
ifelse(y == 0,2*theta,
(1/y)*(exp(y*y + y*theta)
- exp(y*y - y*theta)))
}
unnorm2 <- function(y)
{
## return(unnorm1(c(x,y)))  ##here y is 1-dim
ifelse(y == 0,2*theta,
(1/y)*(exp(x*y + y*theta)
- exp(x*y - y*theta)))
}
}
return(integrate(unnorm2, lower=-theta, upper=theta,

upper=c(theta, theta), functn=unnorm1)\$value)
}

if(pos==2)
{
unnorm <- function(x)
{
ifelse(x==0,4,(exp(2*theta*x)+exp(-2*theta*x) - 2)/(x^2))
}
return(integrate(unnorm,lower = -theta, upper = x,
subdivisions=1000)\$value/
integrate(unnorm,lower = -theta, upper = theta,
subdivisions=1000)\$value)
}
}

```