Autograd Node: Add and Multiply

Problem

Implement one node of a tiny reverse-mode autograd engine.

For z = a * b + c, return [z, dz/da, dz/db, dz/dc]. The multiply node feeds the add node, so gradients flow backwards through both: dz/dc = 1, dz/db = a, and dz/da = b.

Hint

Local gradients multiply along the path and add at branches.

Test cases

case 1

in: [2,3,4]

expected: [10,3,2,1]

case 2

in: [0,-1,5]

expected: [5,-1,0,1]

case 3

in: [1.5,2,0]

expected: [3,2,1.5,1]

case 4

in: [-2,3,1]

expected: [-5,3,-2,1]

Starter codePython

def autograd_addmul(a, b, c):
    # Return [z, dz_da, dz_db, dz_dc]
    # Your code here
    pass

4 test cases · run your code against them in the editor