[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)$value)
}
}
if(len==3)
{
if((pos==1) || (pos==3))
{
unnorm1 <- function(y) ##here y is 2-dim
{
ifelse(y[2] == 0,2*theta,
(1/y[2])*(exp(y[1]*y[2] + y[2]*theta)
- exp(y[1]*y[2] - y[2]*theta)))
}
unnorm2 <- function(y)
{
## return(unnorm1(c(x,y))) ##here y is 1-dim
ifelse(y == 0,2*theta,
(1/y)*(exp(x*y + y*theta)
- exp(x*y - y*theta)))
}
}
return(integrate(unnorm2, lower=-theta, upper=theta,
subdivisions=1000)$value/adapt(ndim=2,lower=c(-theta, -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)
}
}
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