What's the dimension of dA/dZ after vectorized?

In logistic regression, assume n examples in total, so dim(A) = (1, n) = dim(Y) = dim(z).

  1. What is the dimension of dA/dZ?
  2. Why?

(Please note that the symbol da/dz means the derivative of A to Z, which is different from the “dz” in our code.)

Thanks.

The activation function is applied “elementwise”, so the derivatives are also computed “elementwise”. That means that the shape of \displaystyle \frac {\partial A}{\partial Z} is the same shape as A and Z. In Prof Ng’s notation, that would be 1 x m, where m is the number of input samples.