Notes for BBS/Archibald-080709-110259.jpg

Warning. The first term in the definition of [math]\displaystyle{ C }[/math], written on the blackboard as the identity matrix [math]\displaystyle{ I }[/math], should really be the diagonal matrix whose [math]\displaystyle{ jj }[/math] entry is [math]\displaystyle{ -s_jd_j }[/math]. Thus the [math]\displaystyle{ C }[/math] in the example should be [math]\displaystyle{ C=\begin{pmatrix}-1&0&0\\-1&1&1\\0&1&1\end{pmatrix} }[/math].