Confusing notation in Lecture 4b, Slide 7

[davidrosenberg]

In Slide 7 we illustrate a subgradient of a function on reals, in which case the subgradient is a scalar -- the slope of the linear lower bound on the function. But we've written it as a vector. (Exactly analogous to the gradient of a function on reals just being the derivative, which is the slope of the tangent line at a point.)