CPXcopybase

Description

The routine CPXcopybase() is used to copy a basis into a CPLEX problem object. It is not necessary to copy a basis prior to optimizing an LP problem, but a good initial basis can increase the speed of optimization significantly. A basis does not need to be primal or dual feasible to be used by the optimizer.

The basis is ignored by the optimizer if CPX_PARAM_ADVIND is set to CPX_OFF.

When a basis is installed to a linear problem and CPXlpopt() is used with CPX_PARAM_LPMETHOD set to CPX_ALG_AUTOMATIC, CPLEX will use the primal simplex algorithm if the basis is primal feasible and the dual simplex method otherwise.

Return Value

The routine returns a zero on success, and a nonzero if an error occurs.

Synopsis 

  int CPXcopybase (CPXCENVptr env,
                   CPXLPptr lp,
                   const int *cstat,
                   const int *rstat);

Arguments

CPXCENVptr env

The pointer to the CPLEX environment as returned by CPXopenCPLEX().

CPXLPptr lp

A pointer to a CPLEX problem object as returned by CPXcreateprob().

const int *cstat

An array containing the basis status of the columns in the constraint matrix. The length of the array is equal to the number of columns in the problem object.

CPX_AT_LOWER 
0 
variable at lower bound 
CPX_BASIC 
1 
variable is basic 
CPX_AT_UPPER 
2 
variable at upper bound 
CPX_FREE_SUPER 
3 
variable free and non-basic 

Values for cstat[j]:

const int *rstat

An array containing the basis status of the slack/surplus/artificial variable associated with each row in the constraint matrix. The array's length is equal to the number of rows in the CPLEX problem object. For rows other than ranged rows, the array element rstat[i] has the following meaning:

CPX_AT_LOWER 
0 
associated slack/surplus/artificial variable non-basic at value 0.0 
CPX_BASIC 
1 
associated slack/surplus/artificial variable basic 

For ranged rows, the array element rstat[i] has the following meaning:

CPX_AT_LOWER 
0 
associated slack/surplus/artificial variable non-basic at its lower bound 
CPX_BASIC 
1 
associated slack/surplus/artificial variable basic 
CPX_AT_UPPER 
2 
associated slack/surplus/artificial variable non-basic at its upper bound 

Example 

  status = CPXcopybase (env, lp, cstat, rstat);

See Also

CPXreadcopybase()
Example lpex6.c in the CPLEX User's Manual.
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