Off-Diagonal Impact?

Hello, I’m trying to evaluate the impact of a declining inventory. Right now my model estimates the on-diagonal impact (inventory 1 declines by the addition of resource 1), but I’d like it to decline also by the off-diagonal impact (inventory 1 also declines by the addition of resources 2 and 3). Any help would be greatly appreciated!
TestProblem.gms (1.23 KB)