R help - May 2007 - Permanent of a matrix

Hello all,
Does anyone know of a function for calculating the permanent of a matrix? 

I have found only the function for calculating a matrix's determinant, 
and my beginner attempts to figure out a working script (see below) have 
failed.  (That is, I don't get the same answer as when I calculate the 
permanent in Maple or Mathematica.)

My understanding and experience is that it can be an exceedingly 
difficult (memory intensive) calculation for matrices larger than ~24x24 
(which also suggests that there is something wrong in the way I've coded 
this) but I can't seem to figure out where my error lies; whether it's 
in my code or in my understanding of how a matrix permanent is defined.

Thanks in advance
-Mark


perm<-function(A){   
    m<-dim(A)[1]
    M1<-dim(0)
    for (i in 
1:nrow(A)){temp.M<-c(A)[i+0:(m-i)*(m+1)];M1<-c(M1,prod(temp.M))}
   
    M2<-dim(0)
    for (i in 
2:nrow(A)){temp.M<-c(t(A))[i+0:(m-i)*(m+1)];M2<-c(M2,prod(temp.M))}
   
    B<-A[nrow(A):1,]
    M3<-dim(0)
    for (i in 
1:nrow(B)){temp.M<-c(B)[i+0:(m-i)*(m+1)];M3<-c(M3,prod(temp.M))}
   
    M4<-dim(0)
    for (i in 
2:nrow(B)){temp.M<-c(t(B))[i+0:(m-i)*(m+1)];M4<-c(M4,prod(temp.M))}
   
    Perm<-sum(M1,M2,M3,M4)
    Perm
}
S<-4
A<-array(seq(1,S^2),dim=c(S,S))
perm(A)


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