[R] define matrix by outer?

[Zhen Pang]

Dear all,

I'd like to define a k by k matrix where the element is defined by

mn<-function(m,n) sum(choose(m,(m-0:m))*choose((k-m),(n-m+0:m)))

the mn function works fine for scalar m and n, however, it fails to define 
the matrix by outer.

a<-outer(1:k,1:k,mn)

gives error message:

Error in outer(1:k, 1:k, mn) : dim<- : dims [product 64] do not match the 
length of object [1]
In addition: Warning messages:
1: Numerical expression has 64 elements: only the first used in: 0:m
2: Numerical expression has 64 elements: only the first used in: 0:m

I can define this matrix by loop or some apply function, however, the outer 
function should be the most straitforward way. How to deal with it? Thanks.

Regards,

Zhen