% - ``alpha`` -- the optimal step size in the negative gradient
% direction.
%
+ % NOTES:
+ %
+ % It is possible to save one matrix-vector multiplication here, by
+ % taking d_k as a parameter. In fact, if the caller is specialized to
+ % our problem (1), we can avoid both matrix-vector multiplications here
+ % at the expense of some added roundoff error.
+ %
% The gradient of f(x) is Qx - b, and d_k is the negative gradient
% direction.