Network simplex options missing in CPLEX MP

[4er4er4er]

ASL's "netopt" is described in the option listing as

alg:network (network, netopt)
       Solve (substructure of) (MIP node) LPs by network simplex method.

whereas it should correspond to the listing for the ASL version:

netopt                 0 means never invoke the network optimizer.
                       1 (default) means invoke the network optimizer
                         only if the model had node and arc declarations.
                       2 means always invoke the network optimizer
                         (unless there are integer variables); the network
                         optimizer may be able to find and exploit an
                         embedded network.
                       3 is similar to 2, but sets CPLEX's LPMethod
                         to CPX_ALG_NET rather than explicitly invoking
                         the network optimizer.  This might make a
                         difference if CPLEX's presolve makes relevant
                         reductions.

ASL's other network simplex options -- all the other ones that begin with "net" -- are missing from the MP implementation.

(This was reported by a user who upgraded CPLEX and could no longer use netopt=2 and netfind=2 except by switching to cplexasl.)

[glebbelov]

MP does not read node/arc declarations from the NL model currently. Thus, the network structure is not known and the network optimizer cannot be called in general; only CPX_ALG_NET can be used with the usual LP solver. To achieve best network simplex performance, presolve=0 in cplex might be needed.

MP's netopt (no value) equals ASL's netopt=3. @4er4er4er do we need ASL-compatible values, e.g., for netopt only? @mapgccv Why has netopt no values, along with alg:primal, alg:barrier, etc? (They are primalopt, baropt in ASL by the way.)

netfind should be easy to add.

[4er4er4er]

It seems to be more complicated than I thought. When there are node and arc definitions, the output from CPLEX (with default settings) suggests that it received a network structure from ASL. But when there are no node and arc definitions -- as in multi.mod + multi.dat from the book -- netopt 2 activates the network extractor in CPLEX, which looks for a network structure as specified by netfind:

ampl: model multi.mod;
ampl: data multi.dat;
ampl: option solver cplexasl;
ampl: option cplex_options 'netopt 2 netfind 2';
ampl: solve;

Presolve eliminates 7 constraints and 3 variables.
Adjusted problem:
60 variables, all linear
44 constraints, all linear; 165 nonzeros
	29 equality constraints
	15 inequality constraints
1 linear objective; 60 nonzeros.

CPLEX 22.1.1.0: netopt 2
netfind 2

CPLEX 22.1.1.0: optimal solution; objective 199500
Network extractor found 36 nodes and 75 arcs.
46 network simplex iterations.
24 dual simplex iterations (0 in phase I)
ampl: 

It would be interesting to make a version of this model using node and arc definitions for Supply and Demand, plus subject-to definitions for the Multi constraints, and see what happens with various netopt and netfind settings.