1. A computer-implemented method of modeling production for a semiconductor foundry, the method comprising: obtaining a multi-part order including: a first order for a fixed number of preliminary products; and a second order for a fixed number of completed products formed from the fixed number of preliminary products; and determining an amount of inventory required to fulfill the first order and the second order, wherein the determining includes: creating a first model including a first inventory amount required to meet the first order; creating a second model including a second inventory amount required to meet the second order, wherein the second model accounts for results from the first model, including the first inventory amount; and running a single linear programming (LP) process using the first model and the second model to determine the amount of inventory required to fulfill the first order.