PENELITIAN OPERASIONAL I
Lecture 9
Lecture 9
• Outline:
– Analisa Sensitivitas Simplex
– Duality
• References:
– Frederick Hillier and Gerald J. Lieberman. Introduction
to Operations Research. 7th ed. The McGraw-Hill
Companies, Inc, 2001.
– Hamdy A. Taha. Operations Research: An Introduction.
8th Edition. Prentice-Hall, Inc
, 2007.
Sensitivity Analysis
– Objective Function –
• Contoh kasus:
𝑀𝑎𝑥𝑖𝑚𝑖𝑧𝑒 𝑧 = 3𝑥1 + 2𝑥2 + 5𝑥3 𝑠𝑢𝑏𝑗𝑒𝑐𝑡 𝑡𝑜 𝑥1 + 2𝑥2 + 𝑥3 ≤ 430 (𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑜𝑛 1) 𝑥1 + 2𝑥3 ≤ 460 (𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑜𝑛 2) 𝑥1 + 4𝑥2 ≤ 420 (𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑜𝑛 3) 𝑥1, 𝑥2, 𝑥3 ≥ 0• Hasil Optimal:
Basic 𝒙𝟏 𝒙𝟐 𝒙𝟑 𝒙𝟒 𝒙𝟓 𝒙𝟔 Solution 𝒛 4 0 0 1 2 0 1350 𝒙𝟐 -1/4 1 0 1/2 -1/4 0 100 𝒙𝟑 3/2 0 1 0 1/2 0 230 𝒙𝟔 2 0 0 -2 1 1 20𝑥
1= mainan – kereta
𝑥
2= mainan – truk
𝑥
3= mainan - mobil
Shadow Price
• It is often important for managers to determine how a
change in a constraint’s right-hand side changes the
LP’s optimal z-value.
• With this in mind, we define the shadow price for the
i
thconstraint of an LP to be the amount by which the
optimal z-value is improved—increased in a max
problem and decreased in a min problem—if the
right-hand side of the i
thconstraint is increased by 1.
• This definition applies only if the change in the
right-hand side of Constraint i leaves the current basis
6
Contoh: Shadow Price
Shadow price jika resource
b1 bertambah 1 unit
b1 ditambah 1 unit menjadi 9
Nilai z bertambah 4/5 (shadow price) 7 + 4/5 = 39/5 Max x1 3x2 ST 2x13x2 x3 8 x1 x2 x4 1 x1 , x2 , x3, x4 0
D
U
A
L
I
T
A
S
Terima kasih kepada Prof.Dr.Ir. Abdullah Alkaff, M.Sc.
Linear Programming
Linear Programming
Kondisi keoptimalan:
sehingga persoalan LP dapat diintepretasikan sebagai
berikut:
cari y
1, y
2, …, y
msedemikian hingga (1) dan (2)
terpenuhi
z
0= y b = y
1b
1+ y
2b
2+ … + y
mb
m(1)
Linear Programming
Dapat dilakukan dengan menyelesaikan LP sebagai
berikut:
Maka diperoleh problem LP yang baru yang disebut
DUAL dari problem semula atau disingkat PROBLEM
DUAL
Min z
0= y
1b
1+ y
2b
2+ … + y
mb
msubject to
y
1a
1j+y
2a
2j+ … + y
ma
mj
c
jy
1, y
2, y
m
0
Primal and Dual
The dual problem uses exactly the same parameters as the primal problem, but in different location.
Primal Problem
Dual Problem
Max
s.t.
Min
s.t.
n j j jx
c
Z
1,
m i i iy
b
W
1,
a
ijx
j
b
i,
j1 n
m i j i ijy
c
a
1 ,for
i
1
,
2
,
,
m
.
for
j
1
,
2
,
,
n
.
for
i
1
,
2
,
,
m
.
for
j
1
,
2
,
,
n
.
,
0
jx
y
i
0
,
Primal Dual dalam Matriks
Where and are row
vectors but and are column vectors.
c
y
y
1
,
y
2
,
,
y
m
b
x
Primal Problem
Dual Problem
Maximize
subject to
.
0
x
y
0
.
Minimize
subject to
b
Ax
yA
c
,
cx
Z
W
yb
,
Contoh: Primal – Dual
Max
s.t.
Min
s.t.
Primal Problem
in Algebraic Form
in Algebraic Form
Dual Problem
,
5
3
x
1x
2Z
,
18
12
4
y
1y
2y
3W
18
2
3
x
1
x
2
12
2
x
2
4
1
x
0
x
,
0
x
1
2
5
2
2
y
2
y
3
3
3
3
y
1y
0
y
,
0
y
,
0
y
1
2
3
Programa Dual
Hubungan antara PRIMAL dan DUAL adalah sebagai
berikut :
PRIMAL
DUAL
RHS
Fungsi Tujuan
MAX
MIN
Programa Dual
x
1x
2
x
nRHS
y
1a
11a
12
a
1n
b
1y
2a
21a
22
a
2n
b
2y
ma
m1a
m2a
mn
b
m
c
1c
2
c
n
Koefisien Fungsi Objektif (Maksimisasi) Koefisie n Fu ng si Ob jek tif (Min imisa si)
PRIMAL
DUA
L
Contoh Programa Dual
PRIMAL : Max 3x1 + 5x2 s.t. x1 4 2x2 12 3x1 + 2x2 18 x1, x2 0DUAL : Min 4y1 + 12y2 + 18y3 s.t.
y1 + 3y3 3 2y2 + 2y3 5 y1, y2 , y3 0
Primal of Diet problem
Diet Problem – Dual
PRIMAL – DUAL
Secara umum hubungan antara DUAL dan PRIMAL dapat
digambarkan seperti pada tabel di bawah ini
MINIMASI MAKSIMASI
Unrestricted
=
=
UnrestrictedV
ariab
le
V
ariab
le
Co
nstr
ain
t
Constr
aint
Contoh
PRIMAL : Max 8x1 + 3x2 s.t. x1 – 6x2 4 5x1 + 7x2 = – 4 x1 0 x2 0 DUAL : Min 4w1 – 4w2 s.t. w1 + 5w2 8 – 6w1 + 7w2 3 w1 0 w2 unrestrictedContoh 2
RI-1333 OR1/sew/2007/#6
Primal: Max. z = 3x1 + 2x2 (Obj. Func.)
subject to 2x1 + x2 100 (Finishing constraint) x1 + x2 80 (Carpentry constraint) x1 40 (Bound on soldiers) x1, x2 0 Optimal Solution: z = 180, x1 = 20, x2 = 60
Dual : Min. w = 100y1 + 80y2 + 40y3 (Obj. Func.)
subject to
2y1 + y2 + y3 3 y1 + y2 2 y1, y2, y3 0
Complementary Basic Solution
Problem Dual :
Constraint
z
j– c
j
0 ; z
j
c
jz
j– Surplus Var = c
jatau
Surplus Var. = z
j– c
jDalam Tableau
Original Variables
Slack Variables
x
1x
2
x
nx
n+1x
n+2 x
n+mComplementary Basic Solution
PRIMAL VARIABLES
DUAL VARIABLES
Original Variable : x
jz
j– c
j: Surplus Variable
Slack Variable : x
n+iy
i: Original Variable
Basic
Nonbasic
Nonbasic
Basic
Original Variables
Slack Variables
x
1x
2
x
nx
n+1x
n+2 x
n+mBaris 0: z
1– c
1z
2– c
2
z
n– c
ny
1y
2
y
mComplementary Basic Solution
PRIMAL VARIABLES
DUAL VARIABLES
Original Variable : x
jz
j– c
j: Surplus Variable
Slack Variable : x
n+iy
i: Original Variable
Basic
Nonbasic
Nonbasic
Basic
1)
Bila x
j> 0, maka ………..….
2)
Bila x
n+i> 0, maka………….
3)
Bila y
i> 0, maka ……….……
Complementary Basic Solution
Dapat diringkas sebagai berikut:
1. x
n+iy
i= 0
2. (z
j– c
j) x
j= 0
Jadi constraint di satu problem adalah renggang
(non-binding), maka variabel yang berkaitan dengan constrain ini
dalam problem yang lain harus nol.
Contoh:
The Dakota Furniture Company manufactures desk, tables, and chairs. The manufacture of each type of furniture lumber and two types of skilled labor: finishing and carpentry. The amount of each resource needed to make each type of furniture is given in Table
At present, 48 bard feet of lumber, 20 finishing hours, and 8 carpentry hours are available. A desk sells for $60, and a table for $30, and a chair for $20. Dakota believes that demand for desks, chairs and tables is unlimited. Since available resource have already been purchased. Dakota wants to maximize total revenue
Resource Desk Table Chair
Lumber 8 board ft 6 board ft 1 board ft Finishing hours 4 hours 2 hours 1.5 hours Carpentry hours 2 hours 1.5 hours 0.5 hours
0
,
,
8
5
.
0
5
.
1
2
20
5
.
1
2
4
48
6
8
.
.
20
30
60
3 2 1 3 2 1 3 2 1 3 2 1 3 2 1
x
x
x
x
x
x
x
x
x
x
x
x
t
s
x
x
x
z
Max
0
,
,
20
5
.
0
5
.
1
30
5
.
1
2
6
60
2
4
8
.
.
8
20
48
3 2 1 3 2 1 3 2 1 3 2 1 3 2 1
y
y
y
y
y
y
y
y
y
y
y
y
t
s
y
y
y
w
Min
2 2 1.5 0 0.5 8
0 8 0 8 5 . 1 0 2 2 4 20 24 8 1 0 6 2 8 48 8 , 0 , 2 , 280 3 2 1 3 2 1 s s s x x x z
1 0 1.510 0.510 20
0 5 30 10 5 . 1 10 2 0 6 0 60 10 2 10 4 0 8 10 , 10 , 0 , 280 3 2 1 3 2 1 e e e y y y wContoh
0
,
1
8
3
2
Subject to
3
M ax
2 1 2 1 2 1 2 1
x
x
x
x
x
x
x
x
0
,
,
,
1
8
3
2
Subject to
3
M ax
4 3 2 1 4 2 1 3 2 1 2 1
x
x
x
x
x
x
x
x
x
x
x
x
z x1 x2 x3 x4 RHS z 1 -1 -3 0 0 0 x3 0 2 3 1 0 8 x4 0 -1 1 0 1 1 z 1 -4 0 0 3 3 x3 0 5 0 1 -3 5 x2 0 -1 1 0 1 1 z 1 0 0 0.8 0.6 7 x1 0 1 0 0.2 -0.6 1 x2 0 0 1 0.2 0.4 2Hubungan Primal - Dual
Primal
Dual
z x1 x 2 x 3 x4 RHS z 1 -1 -3 0 0 0 x 3 0 2 3 1 0 8 x 4 0 -1 1 0 1 1 z 1 -4 0 0 3 3 x 3 0 5 0 1 -3 5 x 2 0 -1 1 0 1 1 z 1 0 0 0.8 0.6 7 x 1 0 1 0 0.2 -0.6 1 x 2 0 0 1 0.2 0.4 2Hubungan PRIMAL – DUAL
Bila x adalah feasible terhadap PRIMAL dan y feasible
terhadap DUAL, maka cx
yb
Nilai objektif problem Max
Nilai objektif problem
Min
DUAL Constraint
y A
c
x
0 y Ax
cx
Ax
b y b
cx
Teorema Dualitas
● Bila x
*adalah penyelesaian dari PRIMAL dan y
*adalah
penyelesaian dari DUAL, maka cx
*= y
*b
● Bila x
0feasible terhadap PRIMAL dan y
0feasible
terhadap DUAL sedemikian hingga cx
0= y
0b
, maka x
0dan y
0adalah penyelesaian optimal
Menyelesaikan PRIMAL Menyelesaikan DUAL