Course 4 Week 1 Assignment 1 - Exercise 3 - conv_forward

Everything you say above sounds correct, but your results are obviously not correct. Note that your value for Z[0,2,1] is all zeros, but it should not be. Are you sure that you are not skipping any positions in the output? In other words, using the stride in the loop limits would be a mistake. You must touch every position of the output: the skipping caused by the striding happens only in the “input” space, right?

Have you seen this thread, which gives a nice overview of what the code needs to do in conv_forward.