Course 1, Week 4 Programming assignment 1 L-Model Backward

Course Q&A Deep Learning Specialization Neural Networks and Deep Learning
1

The formulas to compute dAl are different in video and in assignment.

In video:

Screen Shot 2021-05-31 at 2.59.07 PM
Screen Shot 2021-05-31 at 2.59.07 PM1870×1058 175 KB

In assignment Building_your_Deep_Neural_Network_Step_by_Step 6.3 - L-Model Backward:

Screen Shot 2021-05-31 at 3.01.03 PM
Screen Shot 2021-05-31 at 3.01.03 PM1974×272 44.9 KB

To my understanding, the formula in the assignment is correct. Could anyone help to confirm?
If I made a mistake, I’m glad to know the right answer.

Thank you.

2

Hey @xfan, the two formulas are equivalent. In the slides, the formula is -y/a + (1-y)/(1-a). In the assignment, it is -(y/a - (1-y)/(1-a)) which simplifies to the same formula in the slides if you apply the minus operator to both terms in the bracket.

3

Thanks for pointing out, you are right. I got distracted by the calculus calculation and forgot the most straightforward transformation.