Question

A factory produces m (i = 1, 2, ..., m) products, each of which requires processing on n (j = 1, 2, ..., n) workstations. Let aij be the amount of processing time that one unit of the ith product requires on the jth workstation. Let the revenue from selling one unit of the ith product be ri and hi be the holding cost per unit per time period for the ith product. The planning horizon consists of T (t = 1, 2,..., T) time periods. The minimum demand that must be satisfied in time period t is dit, and the capacity of the jth workstation in time period t is cjt. Consider the aggregate planning formulation below, with decision variables Sit (amount of product i sold in time period t), Xit (amount of product i manufactured in time period t) and Iit (amount of product i held in inventory at the end of time period t).

m a x t = 1 T i = 1 m ( r i S i t h i I i t )

Subject to

Sit ≥ dit ∀ i, t

< capacity constraint >

< inventory balance constraint >

Xit, Sit, Iit ≥ 0; Ii0 = 0

The capacity constraints and inventory balance constraints for this formulation respectively are

Options :

  1. i m a i j X i t c j t     i , t and I i t = I i , t 1 + X i t d i t     i , t

  2. i m a i j X i t d i t     i , t and I i t = I i , t 1 + X i t S i t     i , t

  3. i m a i j X i t d i t     i , t and  I i t = I i , t 1 + S i t X i t     i , t

  4. i m a i j X i t c j t     j , t and I i t = I i , t 1 + X i t S i t     i , t

Show Answer

Answer :

i m a i j X i t c j t     j , t and I i t = I i , t 1 + X i t S i t     i , t

Solution :

Product (m) → i ... m

Workstation (n) → j ... n

aij = time, ri = selling price, hi = holding cost

T → t = 1, 2, ... T

dit = demand of the product in time t, cjt = capacity of workstation in time t, Sit = Number of products sold in time t, xit = Number of product produced in time t,

Iit = Number of product i hold in inventory at end of period t

Capacity constraint

aijxit ≤ cjt

Inventory constraint

Iit = Ii, t - 1 + xit - Sit

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