symmetric matrix multiplication

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of statfan
Sent: Saturday, October 22, 2011 10:45 PM
To: r-help at r-project.org
Subject: [R] symmetric matrix multiplication

I have a symmetric matrix B (17x17), and a (17x17) square matrix A.  If do
the following matrix multiplication I SHOULD get a symmetric matrix,
however
i don't.  The computation required is:

C = t(A)%*%B%*%A

here are some checks for symmetry

(max(abs(B - t(B))))

[1] 0

C = t(A)%*%B%*%A
(max(abs(C - t(C))))

[1] 3.552714e-15

Any help on the matter would be very much appreciated.