algorithm for initial MIP relaxation

Sets which continuous optimizer will be used to solve the initial relaxation of a MIP.

Purpose

MIP starting algorithm

API	Parameter Name	Name prior to V12.6.0
C	CPXPARAM_MIP_Strategy_StartAlgorithm	CPX_PARAM_STARTALG
C++	IloCplex::Param::RootAlgorithm	RootAlg
Java	IloCplex.Param.RootAlgorithm	RootAlg
.NET	Cplex.Param.RootAlgorithm	RootAlg
OPL	rootalg	rootalg
Python	parameters.mip.strategy.startalgorithm	mip.strategy.startalgorithm
Interactive	mip strategy startalgorithm	mip strategy startalgorithm
Identifier	2025	2025

Description

Sets which continuous optimizer will be used to solve the initial relaxation of a MIP.

The default Automatic setting (0 zero) of this parameter currently selects the concurrent optimizer for root relaxations of mixed integer linear programming models (MILP) and selects the dual simplex optimizer for root relaxations of mixed integer quadratic programming models (MIQP). The Automatic setting may be expanded in the future so that CPLEX chooses the algorithm based on additional characteristics of the model.

For MILP (integer constraints and otherwise continuous variables), all settings are permitted.

For MIQP (integer constraints and positive semi-definite quadratic terms in the objective), settings 5 (Sifting) and 6 (Concurrent) are not implemented; if you happen to choose them, setting 5 (Sifting) reverts to 0 (zero) and setting 6 (Concurrent) reverts to 4.

For MIQCP (integer constraints and positive semi-definite quadratic terms among the constraints), only the setting 0 (zero) Automatic is permitted.

Table 1. Values
Value	Symbol	Meaning
0	`CPX_ALG_AUTOMATIC`	Automatic: let CPLEX choose; default
1	`CPX_ALG_PRIMAL`	Primal Simplex
2	`CPX_ALG_DUAL`	Dual Simplex
3	`CPX_ALG_NET`	Network Simplex
4	`CPX_ALG_BARRIER`	Barrier
5	`CPX_ALG_SIFTING`	Sifting
6	`CPX_ALG_CONCURRENT`	Concurrent (Dual, Barrier, and Primal in opportunistic mode; Dual and Barrier in deterministic mode)