MGOC10H3 Lecture Notes - Lecture 3: List Box, Semicolon

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19 Aug 2016
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MGOC10 Analysis for Decision Making
Lecture 03
Chapter 2 – Solving LP Models with LINDO Solver Suite
Can download LINGO - www.lindo.com student/demo version or from the course
website.
Can also solve Linear Programs with Excel – see textbook Appendix 2.3.
LINGO does not work on MAC.
Some LINGO syntax
There is an “=” after the MAX or MIN in objective. Min = 6*V11+ 2*V12;
LINGO statements end with semicolon
Start program with “MODEL:” end of program with “END”
Arithmetic Operators: Power “^”, Multiply “*”, Division “/”, Addition “+”, Subtraction “-“.
Order of operations applies
Limit of 32 characters in variable name, must begin with A-Z.
To enter £ type “<=”, to enter ³ type “>=”.
Comments may be placed anywhere, comments are denoted by “!” and end with “;”
@FREE(x1) - allows variable x1 to be unrestricted in sign.
@BIN(x1) – specifies that x1 is 0 or 1 (binary)
@GIN(x1) - specifies that x1 is integer
Example - Giapetto’s Woodcarving
LP model
x1 = # soldiers produced each week
x2 = # trains produced each week
Max z = 3x1 + 2x2
ST 2x1 + 1 x2 ≤ 100
1x1 + 1x2 ≤ 80
x1 ≤ 40
x1 ≥ 0 and x2 ≥ 0
LINGO code
MODEL:
! MGTC74 LINGO example;
[OBJ] MAX = 3*X1 + 2*X2;
[FINISH] 2*X1 + X2 <= 100;
[CARPENTRY] X1 + X2 <= 80;
[DEMAND] X1 <= 40;
END
What is the optimal number of soldiers and trains to produce? Profits?
LINGO Output:
Global optimal solution found.
Objective value: 180.0000
Total solver iterations: 2
Variable Value Reduced Cost
X1 20.00000 0.000000
X2 60.00000 0.000000
Row Slack or Surplus Dual Price
OBJ 180.0000 1.000000
FINISH 0.000000 1.000000
CARPENTRY 0.000000 1.000000
DEMAND 20.00000 0.000000
# of soldiers produced = X1 = 20, # of trains produced = X2 = 60, Profits=objective value =$180
1
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Chapter 3 - Sensitivity Analysis using LINGO
Example – 2 product 3 machine problem
A company produces two products using three machines. The profits from each product, the time each
product takes to produce and the amount of time available for each machine is given in the table below.
The objective is to max revenue.
Machine Product 1 Product 2 Hours Available
1 1 0 4
2 0 2 12
3 3 2 18
Revenue $3 $5
LP model
Let Xi = # of product i to produce
Max Z = 3X1 + 5X2
ST X1 £ 4
2X2 £ 12
3X1 + 2X2 £ 18
X1, X2 ³ 0
LINGO code
MODEL:
[OBJ] MAX = 3*X1 + 5*X2;
[MACH1] X1 <= 4;
[MACH2] 2*X2 <= 12;
[MACH3] 3*X1 + 2*X2 <= 18;
END
LINGO output
Global optimal solution found at step: 2
Objective value: 36.00000
Variable Value Reduced Cost
X1 2.000000 0.0000000
X2 6.000000 0.0000000
Row Slack or Surplus Dual Price
OBJ 36.00000 1.000000
MACH1 2.000000 0.0000000
MACH2 0.0000000 1.500000
MACH3 0.0000000 1.000000
(a) What is the optimal solution (revenue? number of product 1 and 2 made?)
What does the slack or surplus mean?
For machine 1, slack or surplus = 2 means there are 2 unused hours
For machine 2, slack or surplus = 0 means there are 0 unused hours
What does dual Price mean?
Dual price for machine 1 = 0, increasing mach 1 hours by 1, Z increase by $0
Dual price for machine 2 = 3/2, increasing mach 2 hours by 1, Z increases by $1.5
Dual price for machine 3 = 1, increasing mach 3 hours by 1, Z increases by $1.
How much would you be willing to pay for 4 more hrs on machine 2?
2
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