[R] Question regarding R plot

[Charles C. Berry]

On Sat, 17 Apr 2010, Akito Y. Kawahara wrote:

> Hi, I am new to R, and have a quick question regarding an R script
> that I received from a kind colleague.
>
> I am trying to determine the "peak" (maximum value) of the graph that
> is plotted when executing the following. There is an input file called
> "rates_values.txt" which begins as:
>
> rateValue
> 0.375693
> 0
> 1.71274
> 0
> 0
> 1.02832
> 0
> 0.16343
> 1.02349
> 0
> 0
> 1.47258
> 0.703522
> 0.390541
> 1.83415
>
>
>
> The script, below, must run with the rates_values.txt in the same dir.
>
> #-------
> rates<-read.table("rates_values.txt",header=T)
> attach(rates)
> scores<-function(x){
>  l<-length(rateValue)
>  total<-0
>  for(i in 1:l){
>    value<-16*rateValue[i]*rateValue[i]*x*exp(-4*rateValue[i]*x)
>    total<-total+value
>  }
>  return(total)
> }
>
>
> #-------
> #preparing the plot
> linewidth=3
> linetype=3
> color="blue"
> xvalue=0.5
>
> plot(scores,xvalue,0,type="n",font.axis=2,xlim=c(xvalue,0))
> curve(scores,xvalue,add=TRUE,col=color,lty=linetype,lwd=linewidth,xlim=c(xvalue,0))
>
> #-------
>
> Can anyone help me figure out how to determine the peak (maximum
> "scores") value in the plot that is generated?


Yes. Anyone who knows something called 'the calculus' could help. And they 
could point out that the 0's in the data really do not matter.

If the 0's are real data that should influence the result, it seems there 
is something wrong with scores() and you might do well to get a consult 
from a statistician.

If you are still determined to solve the problem as stated, see

 	?optimise


Something like

 	optimise( scores, range(rateValue), maximum=TRUE )

should do it.

HTH,

Chuck


It should be about 11.7
> but I would like to get an exact value. This should be a relatively
> easy question, but I'm new to R, and what I have tried doesn't seem to
> work.
>
> Thanks!
>
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> and provide commented, minimal, self-contained, reproducible code.
>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901