In matrix equations，。

it’s very useful to check that the dimensions all match up. To the right of some equations in this chapter， we denote the dimensionality of the matrices in the product， \(\mathbf{x}_{\texttt{out}}\) is N dimensions， where \(\mathbf{x}_{\texttt{in}}\) is M dimensions， and the loss \(J\) is always a scalar. 。