CPXXchgprobtype and CPXchgprobtype

The routine CPXXchgprobtype/CPXchgprobtype changes the current problem to a related problem.

int CPXXchgprobtype( CPXCENVptr env, CPXLPptr lp, int type )

int CPXchgprobtype( CPXCENVptr env, CPXLPptr lp, int type )

Description

The routine CPXXchgprobtype/CPXchgprobtype changes the current problem to a related problem. The problem types that can be used appear in the table.

Table 1. Problem Types
Value	Symbolic Constant	Meaning
`0`	`CPXPROB_LP`	Linear program, no quadratic data stored.
`1`	`CPXPROB_MILP`	Problem both linear and integer constraints on the variables.
`3`	`CPXPROB_FIXEDMILP`	Problem integer variables fixed.
`5`	`CPXPROB_QP`	Problem with quadratic terms in the objective.
`7`	`CPXPROB_MIQP`	Problem with quadratic terms in the objective and integer variables among the constraints.
`8`	`CPXPROB_FIXEDMIQP`	Problem with quadratic terms in the objective and integer variables fixed.
`10`	`CPXPROB_QCP`	Problem with quadratic terms among the constraints.
`11`	`CPXPROB_MIQCP`	Problem with quadratic terms among the constraints and integer variables among the constraints.

In fixed problem types, if the original problem included SOS constraints (special ordered sets), even noninteger variables in those constraints will be fixed; with the variables thus fixed, the SOS constraints will be discarded from the problem.

A mixed integer problem of type CPXPROB_MILP or CPXPROB_MIQP can be changed to a fixed problem (CPXPROB_FIXEDMILP or CPXPROB_FIXEDMIQP), where bounds on integer variables are fixed to the values attained in the integer solution.

CPLEX does not currently permit you to change a mixed integer problem of type CPXPROB_MIQCP to a fixed problem.

A mixed integer problem (or its related fixed type) can also be changed to a continuous problem (CPXPROB_LP, CPXPROB_QP, or CPXPROB_QCP). This change causes any existing ctype values to be permanently discarded from the problem object. For documentation of ctype, see the routine CPXXchgctype and CPXchgctype.

The original mixed integer problem can be recovered from the fixed problem. If the current problem type is CPXPROB_FIXEDMILP or CPXPROB_FIXEDMIQP, any calls to problem modification routines fail. To modify the problem object, the problem type should be changed to CPXPROB_MILP or CPXPROB_MIQP.

Changing a problem from a continuous type to a mixed integer type causes a ctype array to be created such that all variables are considered continuous. A problem of type CPXPROB_MILP, CPXPROB_MIQP, or CPXPROB_MIQCP can be solved only by the routine CPXXmipopt and CPXmipopt even if all of its variables are continuous.

A quadratic problem (CPXPROB_QP, CPXPROB_MIQP, CPXPROB_QCP, or CPXPROB_MIQCP) can be changed to a linear program (CPXPROB_LP), causing any existing quadratic information to be permanently discarded from the problem object. Changing a problem from a linear program (CPXPROB_LP or CPXPROB_MILP) to a quadratic program (CPXPROB_QP or CPXPROB_MIQP) causes an empty quadratic matrix to be created such that the problem is quadratic with the matrix Q = 0.

Arguments

env: A pointer to the CPLEX environment as returned by CPXXopenCPLEX/CPXopenCPLEX.
lp: A pointer to a CPLEX LP problem object as returned by CPXXcreateprob/CPXcreateprob.
type: An integer specifying the desired problem type. See the previous discussion for possible values.

Return

The routine returns 0 (zero) if successful and nonzero if an error occurs.

Example


status = CPXchgprobtype (env, lp, CPXPROB_MILP);