question on graphs and finding area under a curve

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

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