Chapter 6, description of equation 6.4

[bondrewd]

Hi! In chapter 6, equation 6.4, the matrix W is acting on the vector x. The dimension of the matrix is described to be DxF, and the dimension of the vector is D. However, these dimensionalities are incompatible since a DxF matrix cannot be multiplied by a Dx1 vector. It seems to me that F and D have been confused in the text.