Matrix, Dimensions.
n^[1] by m matrics and then added element-wise. On the previous slide, we talked about the dimensions of w, b, dw, and db. Here what we see is that whereas z^[l], as well as a^[l], are of dimension n^[l] by 1, we have now instead that capital Z^[l], as well as capital A^[l], are n^[l] by m. A