For Exercise 7 - update_parameters, I use the general equation provided to calculate W1 from dW1 and learning rate. However my code fails the test case due to wrong W1. With some debugging, when I print:
print(f"{W1.shape},{dW1.shape}")
I get
(1,4),(4,2)
I thought W1 should have the same shape as dW1, did I miss something?
Your understanding of shapes is correct. W1.shape is the same as dW1.shape.
That said, there’s no need for any equation to arrive at W1.
W1 is stored in one of the dictionaries that are passed on as function parameters to update_parameters.
There must be something wrong with your update formulas. Notice that in the particular test case here W1 is 4 x 2, but W2 is 1 x 4. So your dW1 is the correct shape, but then how did W1 end up the wrong shape? Hmmmmm. Sounds like a classic “copy/paste” error to me …
Mystery solved. I had a W2 = W1 = “deep copy of W2 params” further up in the code 
. The wonders of leaving for a while and coming back to look at your code…