[R] question on graphs and finding area under a curve

[Ravi Varadhan]

Hi,

To find the area lying between the curve y = y(x) and 45 degree line (which,
assuming it goes through the origin, is y = x), you can use the following
function based on trapezoidal rule:

trap.rule <- function(x,f) {sum(diff(x)*(f[-1]+f[-length(f)]))/2}

trap.rule(x,f=y-x)

This area will be negative if y(x) is below the 45 degree line.

However, your question is not complete, I think.  You need to specify the
interval of integration. For this you may need to determine the points of
intersection of the two curves, which involves the solution of a fixed point
problem.

Hope this helps,
Ravi.

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch [mailto:r-help-
> bounces at stat.math.ethz.ch] On Behalf Of Renuka Sane
> Sent: Tuesday, August 02, 2005 8:51 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] question on graphs and finding area under a curve
> 
> Question on graphs:
> 
> The default case for drawing a graph in R, is where a little space is left
> on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) -
> -
> there will be some space between the edge of the x-axis and where 0 is
> placed. If I want 0 on the edge, how do I do it in R?
> 
> Area under the curve:
> 
> I have a 45 degree line and a curve above or below it. Is there a way in R
> to find the area between the two?
> 
> Thanks,
> Renuka
> 
> --
> Renuka Sane
> http://www.nyx.net/~rsane
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-
> guide.html