[R] simple matrix calculation

[Kehl Dániel]

Dear list-members,

I have a 9-by-9 matrix lets call it A with first row a11, a12, a13,..., 
a19 etc.
I also have a vector of length 3 (B).
I want to construct a matrix of size 3x3 in the following way:
- divide matrix A to 9 3x3 blocks
- first is
         a11, a12, a13
         a21, a22, a23
         a31, a32, a33
- I want to get rowSums of this A1 matrix
- Multiply A1*B and get a scalar, the first element of my new 3x3 matrix.

I could do that with loop. Can you suggest something that is more 
elegant and faster?

Thank you
Daniel