logmip1b.gms : LogMIP User's Manual Example 1b - Job Scheduling

**Description**

Three jobs (A,B,C) must be executed sequentially in three steps, but not all jobs require all the stages. The objective is to obtain the sequence of tasks which minimizes the completion time. Once a job has started it cannot be interrupted. The objective is to obtain the sequence of task, which minimizes the completion time. In this model we will use the THEN ELSE construct and use only 3 binary variables. Note that only the LOGMIP instructions are different. Ref: Raman & Grossmann, Comp. & Chem. Eng., 18, 7, p.563-578, 1994. Aldo Vecchietti, LogMIP User's Manual, 2007, <a href="http://www.logmip.ceride.gov.ar/files/pdfs/logmip_manual.pdf">http://www.logmip.ceride.gov.ar/files/pdfs/logmip_manual.pdf</a>

**References**

- Vecchietti, A, LogMIP User's Manual, 2007. http://www.logmip.ceride.gov.ar/files/pdfs/logmip_manual.pdf
- Raman, R, and Grossmann, I E, Modeling and Computational Techniques for Logic Based Integer Programming. Computers and Chemical Engineering 18, 7 (1994), 563-578.

**Small Model of Type :** EMP

**Category :** GAMS Model library

**Main file :** logmip1b.gms

$Title LogMIP User's Manual Example 1b - Job Scheduling (LOGMIP1B,SEQ=333) $ontext Three jobs (A,B,C) must be executed sequentially in three steps, but not all jobs require all the stages. The objective is to obtain the sequence of tasks which minimizes the completion time. Once a job has started it cannot be interrupted. The objective is to obtain the sequence of task, which minimizes the completion time. In this model we will use the THEN ELSE construct and use only 3 binary variables. Note that only the LOGMIP instructions are different. Ref: Raman & Grossmann, Comp. & Chem. Eng., 18, 7, p.563-578, 1994. Aldo Vecchietti, LogMIP User's Manual, 2007, http://www.logmip.ceride.gov.ar/files/pdfs/logmip_manual.pdf $offtext SET I /1*3/ J /A,B,C/; POSITIVE VARIABLES X(J),T; VARIABLE Z; EQUATIONS equat1, equat2, equat3, equat4, equat5, equat6, equat7, equat8, equat9, OBJECTIVE; equat1.. T =G= X('A') + 8; equat2.. T =G= X('B') + 5; equat3.. T =G= X('C') + 6; equat4.. X('A')-X('C') =L= -5; equat5.. X('C')-X('A') =L= -2; equat6.. X('B')-X('C') =L= -1; equat7.. X('C')-X('B') =L= -6; equat8.. X('A')-X('B') =L= -5; equat9.. X('B')-X('A') =L= 0; OBJECTIVE.. Z =E= T; MODEL PEQUE1 /ALL/; X.UP(J)=20.; $ONECHO > "%LM.INFO%" * by default the convex hull formulation is used disjunction * equat4 else equat5 disjunction * equat6 else equat7 disjunction * equat8 else equat9 * optional, if not set LOGMIP will find the modeltype suitable modeltype mip $OFFECHO OPTION EMP=LOGMIP; SOLVE PEQUE1 USING EMP MINIMIZING Z;