# [R] Odp: Integration in R

Alaios alaios at yahoo.com
Mon Jan 10 15:50:52 CET 2011

```Thanks a lot :)
Feeling embarassed !
Alex

--- On Mon, 1/10/11, Petr PIKAL <petr.pikal at precheza.cz> wrote:

> From: Petr PIKAL <petr.pikal at precheza.cz>
> Subject: Odp: [R] Integration in R
> To: "Alaios" <alaios at yahoo.com>
> Cc: r-help at r-project.org
> Date: Monday, January 10, 2011, 2:45 PM
> Hi
>
> r-help-bounces at r-project.org
> napsal dne 10.01.2011 15:12:33:
>
> > Dear all,
> >
> > It has been   ages since I studied
> integration in college. Right now I
> > try to recover all this kind of knowledge and then try
> to understand how
> >  integration works.
> >
> >
> >
> > Thus I am doing some first 'experiments' and I would
> like to request
> >
> >
> >
> > I have the function:
> >
> >
> >
> > p2<-function(x){0.5*(3*x^2-1)}
> >
> > # I found the square of p2 by using some pencil and
> paper.
> >
> > # The result is inside myfunc below
> >
> >
> >
> > myfunc<- function(x) {0.25*(9*x^4+6*x^2+1)}
>
> It is quite a long time I did school math but shouldn't be
>
> myfunc<- function(x) {0.25*(9*x^4-6*x^2+1)}
>
>
>    ^^^^^
> myfunc<- function(x) {0.25*(9*x^4-6*x^2+1)}
> curve(myfunc,-1,1)
> integrate(p2sq,-1,+1)
> 0.4 with absolute error < 4.4e-15
> integrate(myfunc,-1,+1)
> 0.4 with absolute error < 4.4e-15
>
> Regards
> Petr
>
>
>
> >
> >
> >
> > # Below I made R to find the square of p2
> >
> > p2sq<-function(x) {p2(x) * p2(x)}
> >
> >
> >
> > # Now I am trying to integrate both two function at
> the same interval.
> #Both
> > functions should denote the square of p2
> >
> >
> >
> > integrate(p2sq,-1,+1)
> >
> > # returns 0.4 with absolute error < 4.4e-15
> >
> >
> >
> > integrate(myfunc,-1,+1)
> >
> > # returns 2.4 with absolute error < 2.7e-14
> >
> >
> >
> > if there is no error in my calculations could you
> > the two integrations return different results. Might
> be that I am
> > missing something from the theory. I would like to
> > help
> >
> >
> >
> > Regards
> >
> > Alex
> >
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