large factorials

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)
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