A single weight gradient is the upstream gradient at the receiving pre-activation times the input activation feeding that weight. This lesson isolates one entry, dw11, so the product can be checked before returning to the full annotated graph.
highlighted = computed this step
Choose one weight
Focus on weight w11. The upstream gradient is dL/dz1=-2, and the input feeding that weight is x1=1. Those two shown values are the source of truth for this one gradient entry.
dz1dL=−2,x1=1
Multiply upstream by input
The local rule for this weight is upstream gradient times the input activation. Here dL/dw11=-2*1=-2. No extra displayed number is supplied; the product is recomputed from the same exact inputs.
dw11dL=−2⋅1=−2
Place the table entry
The single product lands in the gradient table as dw11=-2. This is one displayed gradient entry only: the surrounding table and graph use the same exact reverse-pass register.