This section presents the solution files produced by CPLEX. It includes these topics:
Format of an ASCII-Text Solution File
An ASCII text solution file is created in Concert Technology with the method IloCplex::writeTextSolution, in the Callable Library with the CPXwritesol routine, or in the Interactive Optimizer via the write command. In either case, the file type TXT should be specified. If a file name with a .txt extension is specified, the file type may be omitted. A solution file consists of three sections: heading, rows, and columns.
Heading Section
A heading section in an ASCII-text solution file lists the following information:
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Problem name (usually the problem file name)
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Data name (if given; otherwise, blank)
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Objective value
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Problem status (optimal, nonoptimal, or infeasible)
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Number of iterations required to solve
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Objective name (if given; otherwise, default is obj) and sense (min or max)
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Right-hand side name (if given; otherwise default is rhs)
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Range section name (if given)
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Bound section name (if given)
Rows and Columns Sections
The rows section and the columns section in an ASCII-text solution file are in tabular format. For each row and each column, the file lists the following information:
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NUMBER: An internal number assigned by ILOG CPLEX.
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ROW OR COLUMN: The name assigned to each row or column.
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AT: The status of the row or column; five alternatives exist:
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** Infeasible
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BS basic and feasible
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EQ nonbasic, artificial, or fixed
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UL nonbasic, activity at upper limit
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LL nonbasic, activity at lower limit
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ACTIVITY: The value of the row or column in the solution. For columns, this is simply the value of the variable. For rows, it is the sum of the products of the variable values and coefficient values.
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SLACK ACTIVITY (rows section) or INPUT COST (columns section): For each row, the slack activity is the difference between the RHS value for the row and the row activity. For each column, the input cost is the objective coefficient corresponding to that variable.
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LOWER LIMIT: The lowest activity value for this row or column in this solution which is still feasible.
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UPPER LIMIT: The highest activity value for this row or column in this solution which is still feasible.
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DUAL ACTIVITY (rows section) or REDUCED COST (columns section): The dual activity for a constraint, often called the shadow price, is relevant only for nonbasic constraint activities. The dual activity provides the sensitivity of the objective value to a unit change in a constraint RHS value. The reduced cost for a variable, often called the dj, is relevant only for nonbasic variables. The reduced cost indicates the sensitivity of the objective value to unit changes in the variable value.
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The letter A before any row or column indicates that an alternative optimum is possible.
ILOG CPLEX observes the MPS convention of printing the negative dual variables so that they correspond in sign to the reduced costs in the column section.
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