Transportation Winston 2

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    Transportation, Assignment andTransshipment Problems

    fromOperations Research: Applications & Algorithms,

    4th edition, by Wayne L. Winston

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    Description

    A transportation problem basically deals with the

    problem, which aims to find the best way to fulfill

    the demand of n demand points using the

    capacities of m supply points. While trying to findthe best way, generally a variable cost of shipping

    the product from one supply point to a demand

    point or a similar constraint should be taken into

    consideration.

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    7.1 Formulating Transportation

    ProblemsExample 1: Powerco has three electric

    power plants that supply the electric needs

    of four cities.

    The associated supply of each plant and

    demand of each city is given in the table 1.

    The cost of sending 1 million kwh ofelectricity from a plant to a city depends on

    the distance the electricity must travel.

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    Transportation tableau

    A transportation problem is specified by

    the supply, the demand, and the shipping

    costs. So the relevant data can be

    summarized in a transportation tableau.The transportation tableau implicitly

    expresses the supply and demand

    constraints and the shipping cost between

    each demand and supply point.

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    Table 1. Shipping costs, Supply, and Demand

    for Powerco Example

    From To

    City 1 City 2 City 3 City 4 Supply

    (Million kwh)

    Plant 1 $8 $6 $10 $9 35

    Plant 2 $9 $12 $13 $7 50

    Plant 3 $14 $9 $16 $5 40Demand

    (Million kwh)

    45 20 30 30

    Transportation Tableau

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    Solution

    1. Decision Variable:

    Since we have to determine how much electricity

    is sent from each plant to each city;

    Xij = Amount of electricity produced at plant i

    and sent to city j

    X14 = Amount of electricity produced at plant 1

    and sent to city 4

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    2. Objective function

    Since we want to minimize the total cost of shipping

    from plants to cities;

    Minimize Z = 8X11+6X12+10X13+9X14

    +9X21+12X22+13X23+7X24

    +14X31+9X32+16X33+5X34

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    3. Supply Constraints

    Since each supply point has a limited productioncapacity;

    X11+X12+X13+X14

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    4. Demand Constraints

    Since each supply point has a limited productioncapacity;

    X11+X21+X31 >= 45X12+X22+X32 >= 20

    X13+X23+X33 >= 30

    X14+X24+X34 >= 30

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    5. Sign Constraints

    Since a negative amount of electricity can not be

    shipped all Xijs must be non negative;

    Xij >= 0 (i= 1,2,3; j= 1,2,3,4)

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    LP Formulation of Powercos Problem

    Min Z = 8X11+6X12+10X13+9X14+9X21+12X22+13X23+7X24

    +14X31+9X32+16X33+5X34

    S.T.: X11+X12+X13+X14 = 30

    X14+X24+X34 >= 30

    Xij >= 0 (i= 1,2,3; j= 1,2,3,4)

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    General Description of a Transportation

    Problem

    1. A set of m supply points from which a good is

    shipped. Supply point i can supply at most si

    units.

    2. A set of n demand points to which the good is

    shipped. Demand pointj must receive at least di

    units of the shipped good.

    3. Each unit produced at supply point i and shippedto demand pointj incurs a variable costofcij.

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    Xij = number of units shipped from supply point i to

    demand point j

    ),...,2,1;,...,2,1(0

    ),...,2,1(

    ),...,2,1(..

    min

    1

    1

    1 1

    njmiX

    njdX

    misXts

    Xc

    ij

    mi

    i

    jij

    nj

    j

    iij

    mi

    i

    nj

    j

    ijij

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    Balanced Transportation Problem

    If Total supply equals to total demand, theproblem is said to be a balanced

    transportation problem:

    nj

    j

    j

    mi

    i

    i ds11

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    Balancing a TP if total supply exceeds total

    demand

    If total supply exceeds total demand, we

    can balance the problem by adding dummy

    demand point. Since shipments to thedummy demand point are not real, they are

    assigned a cost of zero.

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    Balancing a transportation problem if total

    supply is less than total demand

    If a transportation problem has a total

    supply that is strictly less than total

    demand the problem has no feasiblesolution. There is no doubt that in such a

    case one or more of the demand will be left

    unmet. Generally in such situations a

    penalty cost is often associated with unmetdemand and as one can guess this time the

    total penalty cost is desired to be minimum

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    7.2 Finding Basic Feasible

    Solution for TPUnlike other Linear Programming

    problems, a balancedTP with m supply

    points and n demand points is easier to

    solve, although it has m + n equality

    constraints. The reason for that is, if a set

    of decision variables (xijs) satisfy all but

    one constraint, the values for xijs willsatisfy that remaining constraint

    automatically.

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    Methods to find the bfs for a balanced TP

    There are three basic methods:

    1. Northwest Corner Method

    2. Minimum Cost Method

    3. Vogels Method

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    1. Northwest Corner Method

    To find the bfs by the NWC method:

    Begin in the upper left (northwest) corner of the

    transportation tableau and set x11 as large as

    possible (here the limitations for setting x11 to a

    larger number, will be the demand of demandpoint 1 and the supply of supply point 1. Your

    x11 value can not be greater than minimum of

    this 2 values).

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    According to the explanations in the previous slide

    we can set x11=3 (meaning demand of demand

    point 1 is satisfied by supply point 1).5

    6

    2

    3 5 2 3

    3 2

    6

    2

    X 5 2 3

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    After applying the same procedure, we saw that we

    can go south this time (meaning demand point 2

    needs more supply by supply point 2).

    3 2 X

    3 2 1

    2

    X X X 3

    3 2 X

    3 2 1 X

    2

    X X X 2

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    Finally, we will have the following bfs, which is:

    x11

    =3, x12

    =2, x22

    =3, x23

    =2, x24

    =1, x34

    =2

    3 2 X

    3 2 1 X

    2 X

    X X X X

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    2. Minimum Cost Method

    The Northwest Corner Method dos not utilize shippingcosts. It can yield an initial bfs easily but the total

    shipping cost may be very high. The minimum cost

    method uses shipping costs in order come up with a

    bfs that has a lower cost. To begin the minimum costmethod, first we find the decision variable with the

    smallest shipping cost (Xij). Then assignXijits largest

    possible value, which is the minimum ofsi and dj

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    After that, as in the Northwest Corner Method we

    should cross out row i and column j and reduce the

    supply or demand of the noncrossed-out row orcolumn by the value of Xij. Then we will choose the

    cell with the minimum cost of shipping from the

    cells that do not lie in a crossed-out row or column

    and we will repeat the procedure.

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    An example for Minimum Cost Method

    Step 1: Select the cell with minimum cost.

    2 3 5 6

    2 1 3 5

    3 8 4 6

    5

    10

    15

    12 8 4 6

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    Step 3: Find the new cell with minimum shipping

    cost and cross-out row 2

    2 3 5 6

    2 1 3 5

    2 8

    3 8 4 6

    5

    X

    15

    10 X 4 6

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    Step 4: Find the new cell with minimum shipping

    cost and cross-out row 1

    2 3 5 6

    5

    2 1 3 5

    2 8

    3 8 4 6

    X

    X

    15

    5 X 4 6

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    Step 5: Find the new cell with minimum shipping

    cost and cross-out column 1

    2 3 5 6

    5

    2 1 3 5

    2 8

    3 8 4 6

    5

    X

    X

    10

    X X 4 6

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    Step 6: Find the new cell with minimum shipping

    cost and cross-out column 3

    2 3 5 6

    5

    2 1 3 5

    2 8

    3 8 4 6

    5 4

    X

    X

    6

    X X X 6

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    Step 7: Finally assign 6 to last cell. The bfs is found

    as: X11=5, X21=2, X22=8, X31=5, X33=4 and X34=6

    2 3 5 6

    5

    2 1 3 5

    2 8

    3 8 4 6

    5 4 6

    X

    X

    X

    X X X X

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    3. Vogels Method

    Begin with computing each row and column a penalty.The penalty will be equal to the difference between

    the two smallest shipping costs in the row or column.

    Identify the row or column with the largest penalty.

    Find the first basic variable which has the smallestshipping cost in that row or column. Then assign the

    highest possible value to that variable, and cross-out

    the row or column as in the previous methods.

    Compute new penalties and use the same procedure.

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    An example for Vogels Method

    Step 1: Compute the penalties.

    Supply Row Penalty

    6 7 8

    15 80 78

    Demand

    Column Penalty 15-6=9 80-7=73 78-8=70

    7-6=1

    78-15=63

    15 5 5

    10

    15

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    Step 3: Identify the largest penalty and assign the

    highest possible value to the variable.

    Supply Row Penalty

    6 7 8

    5 5

    15 80 78

    Demand

    Column Penalty 15-6=9 _ _

    _

    _

    15 X X

    0

    15

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    Step 4: Identify the largest penalty and assign the

    highest possible value to the variable.

    Supply Row Penalty

    6 7 8

    0 5 5

    15 80 78

    Demand

    Column Penalty _ _ _

    _

    _

    15 X X

    X

    15

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    Step 5: Finally the bfs is found as X11=0, X12=5,

    X13=5, and X21=15

    Supply Row Penalty

    6 7 8

    0 5 5

    15 80 78

    15

    Demand

    Column Penalty _ _ _

    _

    _

    X X X

    X

    X

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    7.3 The Transportation Simplex

    Method

    In this section we will explain how the simplex

    algorithm is used to solve a transportation problem.

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    How to Pivot a Transportation Problem

    Based on the transportation tableau, the followingsteps should be performed.

    Step 1. Determine (by a criterion to be developed

    shortly, for example northwest corner method) the

    variable that should enter the basis.

    Step 2. Find the loop (it can be shown that there is

    only one loop) involving the entering variable and

    some of the basic variables.Step 3. Counting the cells in the loop, label them as

    even cells or odd cells.

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    Illustration of pivoting procedure on the Powerco

    example. We want to find the bfs that would result if

    X14 were entered into the basis.

    Nothwest Corner bfs and loop for Powerco

    35 35

    10 20 20 50

    10 30 40

    45 20 30 30

    E O E O E O

    (1, 4) (3, 4) (3, 3) (2, 3) (2, 1) (1, 1)

    0

    12

    34

    5

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    New bfs after X14 is pivoted into basis. Since There

    is no loop involving the cells (1,1), (1,4), (2,1),

    (2,2), (3,3) and (3, 4) the new solution is a bfs.

    35-20 0+20 35

    10+20 20

    20-20

    (nonbasic) 50

    10+20 30-20 40

    45 20 30 30

    After the pivot the new bfs is X11=15, X14=20,

    X21=30, X22=20, X33=30 and X34=10.

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    Two important points!

    In the pivoting procedure:

    1. Since each row has as many +20s as20s, the

    new solution will satisfy each supply and demand

    constraint.

    2. By choosing the smallest odd variable (X23) to

    leave the basis, we ensured that all variables willremain nonnegative.

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    Since the example is a minimization problem, the

    current bfs will be optimal if all the ijs are

    nonpositive; otherwise, we enter into the basis withthe most positive ij.

    After determining cBVB-1 we can easily determine

    ij. Since the first constraint has been dropped,

    cBVB-1 will have m+n-1 elements.cBVB

    -1= [u2 u3um v1 v2vn]

    Where u2 u3um are elements ofcBVB-1

    corresponding to the m-1 supply constraints, and v1v2vn are elements ofcBVB-1 corresponding to the n

    demand constraints.

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    To determine cBVB-1 we use the fact that in any

    tableau, each basic variableXij must have ij=0.

    Thus for each of the m+n-1 variables in BV,

    cBVB-1aijcij=0

    For the Northwest corner bfs of Powerco problem,BV={X11, X21, X22, X23, X33, X34}. Applying the

    equation above we obtain:

    11= [u2 u3 v1 v2 v3 v4] -8 = v1-8=0

    0

    0

    0

    1

    0

    0

    1

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    21= [u2 u3 v1 v2 v3 v4] -9 = u2+v1-9=0

    22= [u2 u3 v1 v2 v3 v4] -12 = u2+v2-12=0

    23= [u2 u3 v1 v2 v3 v4] -13 = u2+v3-13=0

    0

    0

    0

    1

    0

    1

    0

    0

    1

    0

    0

    1

    0

    1

    0

    00

    1

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    u1=0

    u1+v1=8

    u2+v1=9

    u2+v2=12

    u2+v3=13

    u3+v3=16

    u3+v4=5

    By solving the system above we obtain:v1=8, u2=1, v2=11,v3=12, u3=4, v4=1

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    For each nonbasic variable, we now compute

    ij = ui+vjcij

    We obtain:

    12 = 0+116 = 5 13 = 0+1210 = 2

    14 = 0+19 = -8 24 = 1+17 = -531 = 4+814 = -2 32 = 4+119 = 6

    Since 32 is the greatest positive ij, we would nextenter X32 into the basis. Each unit that is entered

    into the basis will decrease Powercos cost by $6.

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    We have determined that X32 should enter the basis. As

    shown in the table below the loop involving X32 and

    some of the basic variables is (3,2), (3,3), (2,3), (2,2).

    The odd cells in the loop are (2,2) and (3,3). Since the

    smallest value of these two is 10 the pivot is 10.

    35 35

    10 20 20 50

    10 30 40

    45 20 30 30

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    The resulting bfs will be:

    X11=35, X32=10, X21=10, X22=10, X23=30 and X34=30

    The uis and vjs for the new bfs were obtained by

    solving

    u1=0

    u2+v2=12

    u3+v4=5

    u1+v1=8

    u2+v3=13

    u2+v1=9

    u3+v2=9

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    7.4 Sensitivity AnalysisIn this section we discuss the following three aspects

    of sensitivity analysis for the transportation problem:

    1. Changing the objective function coefficient of anonbasic variable.

    2. Changing the objective function coefficient of a

    basic variable.

    3. Increasing a single supply by and a single demand

    by .

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    1. Changing the objective function coefficient

    of a nonbasic variable.

    Changing the objective function coefficient of a

    nonbasic variableXij will leave the right hand side of

    the optimal tableau unchanged. Thus the current

    basis will still be feasible. Since we are not changingcBVB

    -1, the uis and vjs remain unchanged. In row 0

    only the coefficient ofXij will change. Thus as long

    as the coefficient ofXij in the optimal row 0 is

    nonpositive, the current basis remains optimal.

    L t t t th f ll i ti b t

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    Lets try to answer the following question about

    Powerco as an example:

    For what range of values of the cost of shipping 1million kwh of electricity from plant 1 to city 1 will the

    current basis remain optimal?

    Suppose we change c11from 8 to 8+ .

    Now 11 = u1+v1-c11=0+6-(8+ )=2- .

    Thus the current basis remains optimal for2- =-2, and c11>=8-2=6.

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    2. Changing the objective function coefficient of a

    basic variable.

    Since we are changing cBVB-1, the coefficient of each

    nonbasic variable in row 0 may change, and to determine

    whether the current basis remain optimal, we must find

    the new uis and vjs and use these values to price out all

    nonbasic variables. The current basis remains optimal as

    long as all nonbasic variables price out nonpositive.

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    Thus, the current basis remains optimal for2

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    7.5. Assignment Problems

    Example: Machineco has four jobs to be completed.

    Each machine must be assigned to complete one job.

    The time required to setup each machine for

    completingeach job is shown in the table below.Machinco wants to minimize the total setup time needed

    to complete the four jobs.

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    The Model

    According to the setup table Machincos problem can be

    formulated as follows (for i,j=1,2,3,4):

    10

    1

    1

    1

    1

    1

    1

    1

    1..

    10629387

    5612278514min

    44342414

    43332313

    42322212

    41312111

    44434241

    34333231

    24232221

    14131211

    4443424134333231

    2423222114131211

    ijij orXX

    XXXX

    XXXX

    XXXX

    XXXX

    XXXX

    XXXX

    XXXX

    XXXXts

    XXXXXXXX

    XXXXXXXXZ

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    For the model on the previous page note that:

    Xij=1 if machine i is assigned to meet the demands of

    jobj

    Xij=0 if machine i is assigned to meet the demands ofjobj

    In general an assignment problem is balancedtransportation problem in which all supplies and

    demands are equal to 1.

    Although the transportation simplex appears to be very

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    Although the transportation simplex appears to be very

    efficient, there is a certain class of transportation

    problems, called assignment problems, for which the

    transportation simplex is often very inefficient. For thatreason there is an other method called The Hungarian

    Method. The steps of The Hungarian Method are as

    listed below:

    Step1. Find a bfs. Find the minimum element in each row

    of the mxm cost matrix. Construct a new matrix by

    subtracting from each cost the minimum cost in its row.

    For this new matrix, find the minimum cost in eachcolumn. Construct a new matrix (reduced cost matrix) by

    subtracting from each cost the minimum cost in its

    column.

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    Step2. Draw the minimum number of lines (horizontal

    and/or vertical) that are needed to cover all zeros in the

    reduced cost matrix. If m lines are required , an optimalsolution is available among the covered zeros in the

    matrix. If fewer than m lines are required, proceed to step

    3.

    Step3. Find the smallest nonzero element (call its value

    k) in the reduced cost matrix that is uncovered by the

    lines drawn in step 2. Now subtract k from eachuncovered element of the reduced cost matrix and add k

    to each element that is covered by two lines. Return to

    step2.

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    7.6 Transshipment Problems

    A transportation problem allows only shipments that godirectly from supply points to demand points. In many

    situations, shipments are allowed between supply points

    or between demand points. Sometimes there may also

    be points (called transshipment points) through whichgoods can be transshipped on their journey from a

    supply point to a demand point. Fortunately, the optimal

    solution to a transshipment problem can be found by

    solving a transportation problem.

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    The following steps describe how the optimal solution to

    a transshipment problem can be found by solving a

    transportation problem.

    Step1. If necessary, add a dummy demand point (with a

    supply of 0 and a demand equal to the problems excess

    supply) to balance the problem. Shipments to the dummyand from a point to itself will be zero. Let s= total

    available supply.

    Step2. Construct a transportation tableau as follows: A

    row in the tableau will be needed for each supply pointand transshipment point, and a column will be needed for

    each demand point and transshipment point.

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    Each supply point will have a supply equal to its

    original supply, and each demand point will have a

    demand to its original demand. Let s= total available

    supply. Then each transshipment point will have a supply

    equal to (points original supply)+s and a demand equal

    to (points original demand)+s. This ensures that anytransshipment point that is a net supplier will have a net

    outflow equal to points original supply and a net

    demander will have a net inflow equal to points original

    demand. Although we dont know how much will beshipped through each transshipment point, we can be

    sure that the total amount will not exceed s.

    Transportation Problem

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    Transportation Problem

    Powerco Power Plant: Formulation

    Define Variables:Let Xij = number of (million kwh) produced at plant i and

    sent to city j.

    Objective Function:Min z = 8*X11 + 6*X12 + 10*X13 + 9*X14

    + 9*X21 + 12*X22 + 13*X23 + 7*X24

    + 14*X31 + 9*X32 + 16*X33 + 5*X34

    Supply Constraints:X11 + X12 + X13 + X14 < = 35 (Plant 1)

    X21 + X22 + X23 + X24 < = 50 (Plant 2)

    X31 + X32 + X33 + X34 < = 40 (Plant 3)

    Transportation

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    pProblem

    Powerco Power Plant: Formulation (Contd.)

    Demand Constraints:X11 + X21 +X31 > = 45 (City 1)

    X12 + X22 +X32 > = 20 (City 2)

    X13 + X23 +X33 > = 30 (City 3)

    X14 + X24 +X34 > = 30 (City 4)

    Nonnegativity Constraints:Xij > = 0 (i=1,..,3; j=1,..,4)

    Balanced?Total Demand = 45 + 20 + 30 + 30 = 125

    Total Supply = 35 + 50 + 40 = 125

    Yes, Balanced Transportation Problem! (If problem is

    unbalanced, add dummy supply or demand as required.)

    Transportation Problem

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    Transportation Problem

    Powerco Power Plant: LINGO Formulation

    model:

    ! A 3 Plant, 4 Customer

    Transportation Problem;

    SETS:

    PLANT / P1, P2, P3/ : CAPACITY;CUSTOMER / C1, C2, C3, C4/ : DEMAND;

    ROUTES( PLANT, CUSTOMER) : COST, QUANTITY;

    ENDSETS

    ! The objective;

    [OBJ] MIN = @SUM( ROUTES: COST * QUANTITY);

    Transportation Problem

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    Transportation ProblemPowerco Power Plant: LINGO Formulation (Contd.)

    ! The demand constraints;

    @FOR( CUSTOMER( J): [DEM]

    @SUM( PLANT( I): QUANTITY( I, J))>= DEMAND( J));

    ! The supply constraints;

    @FOR( PLANT( I): [SUP]

    @SUM( CUSTOMER(J): QUANTITY(I,J))

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    Transportation ProblemPowerco Power Plant: LINGO Solution

    Optimal solution found at step: 7Objective value: 1020.000

    QUANTITY( P1, C1) 0.0000000

    QUANTITY( P1, C2) 10.00000

    QUANTITY( P1, C3) 25.00000QUANTITY( P1, C4) 0.0000000

    QUANTITY( P2, C1) 45.00000

    QUANTITY( P2, C2) 0.0000000

    QUANTITY( P2, C3) 5.000000

    QUANTITY( P2, C4) 0.0000000QUANTITY( P3, C1) 0.0000000

    QUANTITY( P3, C2) 10.00000

    QUANTITY( P3, C3) 0.0000000

    QUANTITY( P3, C4) 30.00000

    All Quantities

    are Integers!

    Transportation Problem

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    Transportation ProblemPowerco Power Plant: LINGO Solution (Contd.)

    Row Slack or Surplus Dual Price

    OBJ 1020.000 1.000000

    DEM( C1) 0.0000000 -9.000000

    DEM( C2) 0.0000000 -9.000000

    DEM( C3) 0.0000000 -13.00000DEM( C4) 0.0000000 -5.000000

    SUP( P1) 0.0000000 3.000000

    SUP( P2) 0.0000000 0.0000000

    SUP( P3) 0.0000000 0.0000000

    All constraints are binding!(Typical of Balanced Transportation Problems; results in

    simple algorithms)

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    Powerco Power Plant: Sensitivity Analysis (Contd.)V i bl V l R d d C t

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    Variable Value Reduced Cost

    QUANTITY( P1, C1) 0.00 2.00 (c11)

    QUANTITY( P1, C2) 10.00 0.00 (c12)

    QUANTITY( P1, C3) 25.00 0.00 (c13)

    QUANTITY( P1, C4) 0.00 7.00 (c14)

    QUANTITY( P2, C1) 45.00 0.00 (c21)

    QUANTITY( P2, C2) 0.00 3.00 (c22)

    QUANTITY( P2, C3) 5.00 0.00 (c23)QUANTITY( P2, C4) 0.00 2.00 (c24)

    QUANTITY( P3, C1) 0.00 5.00 (c31)

    QUANTITY( P3, C2) 10.00 0.00 (c32)

    QUANTITY( P3, C3) 0.00 3.00 (c33)QUANTITY( P3, C4) 30.00 0.00 (c34)

    z = c11* Q11 + c12* Q12 + c13* Q13 + c14* Q14

    + c21* Q21 + c22* Q22 + c23* Q23 + c24* Q24

    + c31* Q31 + c32* Q32 + c33* Q33 + c34* Q34

    Nonbasic

    Basic

    Basic

    Nonbasic

    Basic

    Nonbasic

    BasicNonbasic

    Nonbasic

    Basic

    NonbasicBasic

    A i t P bl

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    Assignment ProblemsPersonnel Assignment:

    Time (hours)

    Job 1 Job 2 Job 3 Job 4

    Person 1 14 5 8 7

    Person 2 2 12 6 5Person 3 7 8 3 9

    Person 4 2 4 6 10

    Assignment Problem Formulation

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    Assignment Problem Formulation

    Define Variables:

    Let Xij = 1 if ith person is assigned to jth job

    Xij = 0 if ith person is not assigned to jth job

    Objective Function:

    Min z = 14*X11 + 5*X12 + + 10*X44Personnel Constraints:

    X11 + X12 + X13 + X14 = 1

    X21 + X22 + X23 + X24 = 1

    X31 + X32 + X33 + X34 = 1X41 + X42 + X43 + X44 = 1

    Demand Constraints:

    X11 + X21 + X31 + X41 = 1

    X12 + X22 + X32 + X42 = 1

    X13 + X23 + X33 + X43 = 1X14 + X24 + X34 + X44 = 1

    Binary Constraints:

    Xij = 0 or Xij = 1

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    Assignment Problem Algorithm

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    Assignment Problem Algorithm

    9 0 3 00 10 4 1

    4 5 0 4

    0 2 4 6

    Subtract Column Minimum from Each Column:

    10 0 3 0

    0 9 3 05 5 0 4

    0 1 3 5

    Subtract Minimum uncrossed value from uncrossed valuesand add to twice-crossed values:

    Draw lines to cross out zeros and read solution from zeros

    0

    00

    0

    Solution:

    Hungarian Method

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    gStep 1: Find the minimum element in each row of the m x m cost

    matrix. Construct a new matrix by subtracting from each cost the

    minimum cost in its row. For this new matrix, find the minimum cost ineach column. Construct a new matrix (called the reduced cost matrix)

    by subtracting from each cost the minimum cost in its column.

    Step 2: Draw the minimum number of lines (horizontal and/or vertical)

    that are needed to cover all the zeros in the reduced cost matrix. If mlines are required, an optimal solution is available among the covered

    zeros in the matrix. If fewer than m lines are needed, proceed to Step

    3.

    Step 3: Find the smallest nonzero element (call its value k) in the

    reduced cost matrix that is uncovered by the lines drawn in Step 2.Now subtract k from each uncovered element of the reduced cost

    matrix and add k to each element that is covered by two lines. Return

    to Step 2