Addlbfgs

Huh. I wonder if this is a correction in the second edition? I only have the first. My version says

sk = x_k+1 - x_k    y_k = g_{k+1} - f_k

and then says 

gamma_k = s_{k-1}^T y_{k-1} / (y_{k-1}^T y_{k-1}) 

At the first iteration, to compute s_{k-1}, we would need to have the s_k from one iteration earlier than the first (which we obviously do not have).  I'm happy to call it gamma instead of prevGamma. Sorry if I'm being dense.