[R] Alternatives to integrate?

. . xkziloj at gmail.com
Thu Sep 1 18:37:51 CEST 2011

```So, please excuse me Michael, you are completely sure. I will try
describe I am trying to do, please let me know if I can provide more
info.

The idea is provide to "func" two probability density functions(PDFs)
and obtain another PDF that is a compound of them. In a final analysis
this characterize an abundance distribution for me. The two PDFs are
provided through "f" and "g" and there is some manipulation here
because I need flexibility to easily change this two funcions.

In the code provided, "f" is the Exponential distribution and "g" is
the Poisson distribution. For this case, I have the analytical
solution, below. This way I can check the result. But I am also
considering other combinations of  "f" and "g" that have difficult, or
even does not have analitical solution. This is the reason why I am
trying to develop "func".

func2 <- function(y, frac, rate, trunc=0, log=FALSE) {
is.wholenumber <- function(x, tol = .Machine\$double.eps^0.5)
abs(x - round(x)) < tol
if(FALSE %in% sapply(y,is.wholenumber))
print("y must be integer because dpoix is a discrete PDF.")
else {
f <- function(y){
b <- y*log(frac)
m <- log(rate)
n <- (y+1)*log(rate+frac)
if(log)b+m-n else exp(b+m-n)
}
f(y)/(1-f(trunc))
}
}
> func2(200,0.05,0.001)
[1] 0.000381062

In theory, the interval of integration is 0 to Inf, but for some tests
I did, go up to 2000 may still provide reasonable results.

Also, as it seems, I am still writing my first functions in R and

Again, appologies for my previous mistake. It was not my intention to

On Thu, Sep 1, 2011 at 11:49 AM, R. Michael Weylandt
<michael.weylandt at gmail.com> wrote:
> I'm going to try to put this nicely:
>
> What you provided is not a problem with integrate. Instead, you provided a
> rather unintelligible and badly-written piece of code that (miraculously)
> seems to work, though it's not well documented so I have no idea if 1.3e-21
> is what you want to get.
>
> Let's try this again: per your original request, what is the problem with
> integrate?
>
> If instead you feel there's something wrong with your code, might I suggest
> you just say that and ask for help, rather than passing the blame onto a
> perfectly useful base function.
>
> Oh, and since you asked that I propose something: comment your code.
>
> Michael
>
> On Thu, Sep 1, 2011 at 10:33 AM, . . <xkziloj at gmail.com> wrote:
>>
>> Hi Michael,
>>
>> This is the problem:
>>
>> func <- Vectorize(function(x, a, sad, samp="pois", trunc=0, ...) {
>>  result <- function(x) {
>>    f1 <- function(n) {
>>                        f <- function() {
>>        dcom <- paste("d", sad, sep="")
>>        dots <- c(as.name("n"), list(...))
>>        do.call(dcom, dots)
>>                        }
>>      g <- function() {
>>        dcom <- paste("d", samp, sep="")
>>        lambda <- a * n
>>        dots <- c(as.name("x"), as.name("lambda"))
>>        do.call(dcom, dots)
>>      }
>>      f() * g()
>>    }
>>    integrate(f1,0,2000)\$value
>>
>> #     n <- 0:2000
>> #     trapz(n,f1(n))
>>
>> #     area(f1, 0, 2000, limit=10000, eps=1e-100)
>>  }
>>  return(result(x) / (1 - result(trunc)))
>> }, "x")
>> func(200, 0.05, "exp", rate=0.001)
>>
>> If you could propose something I will be gratefull.
>>
>>
>> On Thu, Sep 1, 2011 at 10:55 AM, R. Michael Weylandt
>> <michael.weylandt at gmail.com> wrote:
>> > Mr ". .",
>> >
>> > MASS::area comes to mind but it may be more helpful if you could say
>> > what
>> > you are looking for / why integrate is not appropriate it is for
>> > whatever
>> > you are doing.
>> >
>> > Strictly speaking, I suppose there are all sorts of "alternatives" to
>> > integrate() if you are willing to be really creative and build something
>> > from scratch: diff(), cumsum(), lm(), hist(), t(), c(), ....
>> >
>> > Michael Weylandt
>> >
>> > On Thu, Sep 1, 2011 at 9:53 AM, B77S <bps0002 at auburn.edu> wrote:
>> >>
>> >> package "caTools"
>> >> see ?trapz
>> >>
>> >>
>> >> . wrote:
>> >> >
>> >> > Hi all,
>> >> >
>> >> > is there any alternative to the function integrate?
>> >> >
>> >> > Any comments are welcome.
>> >> >
>> >> > Thanks in advance.
>> >> >
>> >> > ______________________________________________
>> >> > R-help at r-project.org mailing list
>> >> > https://stat.ethz.ch/mailman/listinfo/r-help
>> >> > http://www.R-project.org/posting-guide.html
>> >> > and provide commented, minimal, self-contained, reproducible code.
>> >> >
>> >>
>> >> --
>> >> View this message in context:
>> >>
>> >> http://r.789695.n4.nabble.com/Alternatives-to-integrate-tp3783624p3783645.html
>> >> Sent from the R help mailing list archive at Nabble.com.
>> >>
>> >> ______________________________________________
>> >> R-help at r-project.org mailing list
>> >> https://stat.ethz.ch/mailman/listinfo/r-help