From: Ravi Varadhan <rvaradha_at_jhsph.edu>

Date: Tue 02 Aug 2005 - 23:24:05 EST

R-help@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 Received on Tue Aug 02 23:33:53 2005

Date: Tue 02 Aug 2005 - 23:24:05 EST

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@stat.math.ethz.ch [mailto:r-help-
**> bounces@stat.math.ethz.ch] On Behalf Of Renuka Sane
**> Sent: Tuesday, August 02, 2005 8:51 AM
**> To: r-help@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@stat.math.ethz.ch mailing list
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**> PLEASE do read the posting guide! http://www.R-project.org/posting-
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R-help@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 Received on Tue Aug 02 23:33:53 2005

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