[R] large factorials

[Gabor Grothendieck]

sympy() returns a character string, not an R numeric -- it shouldn't
automatically return an R numeric since R can't represent all
the numbers that sympy can.

The development version of rSymPy has a second class which
produces objects of class c("Sym", "character") and those
can be manipulated with +, -, *, / producing other Sym
objects so try this:


library(rSymPy)

# next line pulls in code to handle Sym objects
source("http://rsympy.googlecode.com/svn/trunk/R/Sym.R")

# define factorial to return a Sym object
factorial.Sym <- function(n) Sym("factorial(", n, ")")

sum1 <- function(l,u,t,i,n,w) {
 v <- 0
 for (m in 0 :w) {
	 v1 <- ((u^(1/2))*(l^(1/2))*t)^(i-n+2*m)
	 v2 <- (factorial.Sym(i-n+m))*(factorial.Sym(m))
	 v3 <- v1/v2
	 v <- v+v3
 }
 sympy(v)
}

s <- sum1(1,2,10,80,3,80)
s # Sym object
as.numeric(s) # numeric


On Thu, Apr 23, 2009 at 10:00 AM, molinar <sky2k2 at hotmail.com> wrote:
>
> Here is what I did:
> library(rSymPy)
> factorial.sympy <- function(n) sympy(paste("factorial(", n, ")"))
> factorial.sympy(171)
> [1]
> "1241018070217667823424840524103103992616605577501693185388951803611996075221691752992751978120487585576464959501670387052809889858690710767331242032218484364310473577889968548278290754541561964852153468318044293239598173696899657235903947616152278558180061176365108428800000000000000000000000000000000000000000"
>>
> Which work perfectly.
>
> Here is one of my summation functions:
>
> sum1 <- function(l,u,t,i,n,w) {
> + v <- 0
> + for (m in 0 :w) {
> + v1 <- ((u^(1/2))*(l^(1/2))*t)^(i-n+2*m)
> + v2 <- (factorial.sympy(i-n+m))*(factorial.sympy(m))
> + v3 <- v1/v2
> + v <- v+v3
> + }
> + return(v)
> + }
>
> sum1(1,2,10,80,3,80)
> Error in (factorial.sympy(i - n + m)) * (factorial.sympy(m)) :
>  non-numeric argument to binary operator
>
> I'm not sure why it works when I do the factorial normally but when I call
> my function it doesn't work?
>
>
>
>
>
>
>
> molinar wrote:
>>
>> Thank you everyone all of your posts were very helpful.  I tried each one
>> and I think I have about 10 new packages installed.  The formula I need to
>> calculate did not involve any logarithms but infinite summations of
>> factorials, I'm sorry for not specifying.  I read some things about using
>> logarithms but I thought in my case I would have to do an e to the log and
>> by doing that R still gave me the same problems with numbers over 170.
>>
>> But I was able to get it to work by using the last post about the rsympy
>> packages.
>>
>> I tried downloading bc but I didn't know how to connect it to R, so R said
>> "could not find function bc".
>>
>> Thanks again for all of your help.
>> Samantha
>>
>>
>>
>>
>>
>> Gabor Grothendieck wrote:
>>>
>>> Also the R sympy package can handle this:
>>>
>>>> library(rSymPy)
>>> Loading required package: rJava
>>>
>>>> factorial.sympy <- function(n) sympy(paste("factorial(", n, ")"))
>>>
>>>> # note that first time sympy is called it loads java, jython and sympy
>>>> # but on subsequent calls its faster.  So make a dummy call first.
>>>> factorial.sympy(10)
>>> [1] "3628800"
>>>
>>>> # code from earlier post defining factorial.bc to be inserted here
>>>
>>>>    benchmark(replications=10, columns=c('test', 'elapsed'),
>>> +       bc=factorial.bc(500),
>>> +       sympy = factorial.sympy(500))
>>>    test elapsed
>>> 1    bc    2.17
>>> 2 sympy    0.09
>>>
>>> See the rSymPy, r-bc and rbenchmark home pages:
>>> http://rsympy.googlecode.com
>>> http://r-bc.googlecode.com
>>> http://rbenchmark.googlecode.com
>>>
>>> On Wed, Apr 22, 2009 at 3:21 PM, molinar <sky2k2 at hotmail.com> wrote:
>>>>
>>>> I am working on a project that requires me to do very large factorial
>>>> evaluations.  On R the built in factorial function and the one I created
>>>> both are not able to do factorials over 170.  The first gives an error
>>>> and
>>>> mine return Inf.
>>>>
>>>> Is there a way to have R do these larger calculations (the calculator in
>>>> accessories can do 10000 factorial and Maple can do even larger)
>>>> --
>>>> View this message in context:
>>>> http://www.nabble.com/large-factorials-tp23175816p23175816.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
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>>
>>
>
> --
> View this message in context: http://www.nabble.com/large-factorials-tp23175816p23197344.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
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>