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 physical semiconductor wafers; and a second order for a fixed number of physical semiconductor modules formed from the fixed number of physical semiconductor wafers; 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; creating a supplemental component part number for the second inventory amount required to meet the second order; consigning the first inventory amount required to meet the first order back to the supplemental component part number, wherein a material balance constraint for the supplemental component part number is modeled according to the following: I jma = I ( j - 1 ) ⁢ ma + ∑ k ⁢ ⁢ ∑ q ⁢ ⁢ F jmakq - ∑ n ⁢ ⁢ st. m is ⁢ ⁢ a ⁢ ⁢ component of ⁢ ⁢ n ⁢ ⁢ ∑ e ⁢ ⁢ QTYPER jmaen ⁢ P jnae wherein: I: an inventory; P: a production amount; F: a shipment amount; j: a time period for shipment; m: a material type; a: plant location; n: a material being substituted; e: a process type; k: a demand center location; r: a new material; QTYPER: quantity of a part number and q: a demand class which indicates relative priority of operations; 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 for the fixed number of physical semiconductor wafers.