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Help on solving the linear programming model using solver
Can anyone help solve the following program model? I'm really not sure
what to do but I do have to use solver. The N-P hard problem is: Pm/rj/ WjCjj A set of n=25 jobs and a set of m=4 machines and processing times Pij (the processing time of job j on the machine i), i = 1, Ś,4, j = 1,Ś, 25; job weights w1,Ś,w25. Objective: Schedule the jobs on the 4 machines so that wjCj is minimized, where Cj is the completion time of job j. The basic idea is to introduce an interval-indexed linear program, akin to the time indexed linear program of the previous subsection. Let ďo = 1, and let ďl =2 l-1 , l = 1,Ś,L, where L is large enough that every feasible schedule of interest completes by time 2 L-1 . (By a slight abuse of notation, we let (ďo,ď1) = (1,1) indicate the point interval (1,1)). Let: Xijl = 1, if Jj is assigned to Mi to complete in interval (ďl--1ďl) 0, otherwise, For i = 1,Ś,4, j = 1,Ś,25 and l = 1,Ś,L, let Pij be the processing time of Jj on Mi, for all i,j. We can then write down the following linear programming formulation whose objective function gives a lower bound on the total weighted completion time: Min ďl-1Xijl Subject to 1) Xijl = 1 j = 1,Ś,25 2) PijXijl ¤ ďl, i = 1,Ś,4, l = 1,Ś,L 3) Xijl = 0 if rji,j,l + pij ďl , i,j,l 4) Xijl Ľ 0 i,j,l Observe that the machine load constraints (2) are sufficient relaxed to accommodate the possibility that a job could start a time zero and yet contribute to the load of interval (ďl--1ďl) ; thus any solution vector x corresponding to an integral, feasible schedule is feasible for this LP. Further observe that if Jj completes in (ďl--1ďl) then its contribution to the objective function is wjďl1, a lower bound on its contribution to the actual schedule. |
#3
Posted to microsoft.public.excel.programming
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Help on solving the linear programming model using solver
sorry not .org
plz refer to www.ampl.com -- msn --------------------------------------------- the best time to plant a tree was twenty years ago. the second best time, is today - Chinese proverb "papachunks" wrote: Can anyone help solve the following program model? I'm really not sure what to do but I do have to use solver. The N-P hard problem is: Pm/rj/ WjCjj A set of n=25 jobs and a set of m=4 machines and processing times Pij (the processing time of job j on the machine i), i = 1, Ś,4, j = 1,Ś, 25; job weights w1,Ś,w25. Objective: Schedule the jobs on the 4 machines so that wjCj is minimized, where Cj is the completion time of job j. The basic idea is to introduce an interval-indexed linear program, akin to the time indexed linear program of the previous subsection. Let ďo = 1, and let ďl =2 l-1 , l = 1,Ś,L, where L is large enough that every feasible schedule of interest completes by time 2 L-1 . (By a slight abuse of notation, we let (ďo,ď1) = (1,1) indicate the point interval (1,1)). Let: Xijl = 1, if Jj is assigned to Mi to complete in interval (ďl--1ďl) 0, otherwise, For i = 1,Ś,4, j = 1,Ś,25 and l = 1,Ś,L, let Pij be the processing time of Jj on Mi, for all i,j. We can then write down the following linear programming formulation whose objective function gives a lower bound on the total weighted completion time: Min ďl-1Xijl Subject to 1) Xijl = 1 j = 1,Ś,25 2) PijXijl ¤ ďl, i = 1,Ś,4, l = 1,Ś,L 3) Xijl = 0 if rji,j,l + pij ďl , i,j,l 4) Xijl Ľ 0 i,j,l Observe that the machine load constraints (2) are sufficient relaxed to accommodate the possibility that a job could start a time zero and yet contribute to the load of interval (ďl--1ďl) ; thus any solution vector x corresponding to an integral, feasible schedule is feasible for this LP. Further observe that if Jj completes in (ďl--1ďl) then its contribution to the objective function is wjďl1, a lower bound on its contribution to the actual schedule. |
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