# [R] Odp: Integration in R

Petr PIKAL petr.pikal at precheza.cz
Mon Jan 10 15:45:03 CET 2011

```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 please explain me why
> the two integrations return different results. Might be that I am
> missing something from the theory. I would like to thank you for your
> help
>
>
>
> Regards
>
> Alex
>
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