# GUROBI Options¶

```
ampl: option solver gurobi; # change the solver
ampl: option gurobi_options 'option1=value1 option2=value2'; # specify options
ampl: solve; # solve the problem
```

Solver options obtained with `$ gurobi -=`

.

```
Gurobi Optimizer Options for AMPL
-----------------------------------
To set these options, assign a string specifying their values to the AMPL
option "gurobi_options". For example:
ampl: option gurobi_options 'opttol=1e-6';
Options:
acc:abs
Solver acceptance level for 'AbsConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:and (acc:forall)
Solver acceptance level for 'AndConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:cos
Solver acceptance level for 'CosConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:exp
Solver acceptance level for 'ExpConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:expa (acc:expA)
Solver acceptance level for 'ExpAConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:indeq (acc:indlineq)
Solver acceptance level for 'IndicatorConstraintLinEQ', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:indge (acc:indlinge)
Solver acceptance level for 'IndicatorConstraintLinGE', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:indle (acc:indlinle)
Solver acceptance level for 'IndicatorConstraintLinLE', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:log
Solver acceptance level for 'LogConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:loga (acc:logA)
Solver acceptance level for 'LogAConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:max
Solver acceptance level for 'MaxConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:min
Solver acceptance level for 'MinConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:or (acc:exists)
Solver acceptance level for 'OrConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:pl (acc:pwl, acc:piecewise)
Solver acceptance level for 'PLConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:pow
Solver acceptance level for 'PowConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:quadeq
Solver acceptance level for 'QuadConEQ', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:quadge
Solver acceptance level for 'QuadConGE', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:quadle
Solver acceptance level for 'QuadConLE', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:sin
Solver acceptance level for 'SinConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:sos2
Solver acceptance level for 'SOS2Constraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
acc:tan
Solver acceptance level for 'TanConstraint', default 2:
0 - Not accepted natively, automatic redefinition will be attempted
1 - Accepted but automatic redefinition will be used where possible
2 - Accepted natively and preferred
alg:basis (basis)
Whether to use or return a basis:
0 - No
1 - Use incoming basis (if provided)
2 - Return final basis
3 - Both (1 + 2 = default)
Note that if you provide a valid starting extreme point, either through
primal/dual status, or through warmstart, then Gurobi LP presolve will
be disabled. For models where presolve greatly reduces the problem size,
this might hurt performance.
For problems with integer variables or quadratic constraints,
alg:basis=0 is assumed quietly unless mip:basis=1 or qcp:dual=1 is
specified, respectively.
alg:concurrentmethod (concurrentmethod)
Controls the methods used by the concurrent continuous solver:
-1 - Automatic (default)
0 - Barrier, dual, primal simplex
1 - Barrier and dual simplex
2 - Barrier and primal simplex
3 - Dual and primal simplex
alg:cutoff (cutoff)
If the optimal objective value is worse than cutoff, report "objective
cutoff" and do not return a solution. Default: Infinity for minimizing,
-Infinity for maximizing.
alg:feasrelax (feasrelax)
Whether to modify the problem into a feasibility relaxation problem:
0 = No (default)
1 = Yes, minimizing the weighted sum of violations
2 = Yes, minimizing the weighted sum of squared violations
3 = Yes, minimizing the weighted count of violations
4-6 = Same objective as 1-3, but also optimize the original objective,
subject to the violation objective being minimized.
Weights are given by suffixes .lbpen and .ubpen on variables and .rhspen
on constraints (when nonnegative, default values = 0), else by keywords
alg:lbpen, alg:ubpen, and alg:rhspen, respectively (default values = 1).
Weights < 0 are treated as Infinity, allowing no violation.
alg:feasrelaxbigm (feasrelaxbigm)
Value of "big-M" sometimes used with constraints when doing a
feasibility relaxation. Default = 1e6.
alg:feastol (feastol)
Primal feasibility tolerance (default 1e-6).
alg:global (global)
Synonym for pre:funcnonlinear.
alg:iisfind (iisfind, iis)
Whether to find and export an IIS. Default = 0 (don't export).
alg:iisforce (iisforce)
0/1*: whether to consider the .iis(lb/ub)force suffixes on variables and
range constraints, as well as .iisforce on other constraints. Suffix
values mean the following (ATTENTION: different to Gurobi IIS...Force
attribute!):
-1 - This model item never to be in an IIS (careful, the remaining
constraints can be feasible)
0 - No influence on this bound or constraint (default)
1 - This model item always to be in the computed IIS.
alg:iismethod (iismethod)
Which method to use when finding an IIS (irreducible infeasible set of
constraints, including variable bounds):
-1 - Automatic choice (default)
0 - Often faster than method 1
1 - Can find a smaller IIS than method 0
2 - Ignore the bound constraints.
alg:kappa (kappa, basis_cond)
Whether to return the estimated condition number (kappa) of the optimal
basis (default 0): sum of 1 = report kappa in the result message; 2 =
return kappa in the solver-defined suffix .kappa on the objective and
problem. The request is ignored when there is no optimal basis.
alg:lbpen (lbpen)
See alg:feasrelax.
alg:method (method, lpmethod, simplex)
Which algorithm to use for non-MIP problems or for the root node of MIP
problems:
-1 - Automatic (default): 3 for LP, 2 for QP, 1 for MIP
0 - Primal simplex
1 - Dual simplex
2 - Barrier
3 - Nondeterministic concurrent (several solves in parallel)
4 - Deterministic concurrent
5 - Deterministic concurrent simplex.
alg:networkalg (networkalg)
Whether to use network simplex if an LP is a network problem:
-1 - Automatic choice (default)
0 - No
1 - Yes.
alg:numericfocus (numericfocus, numfocus)
How much to try detecting and managing numerical issues:
0 - Automatic choice (default)
1-3 - Increasing focus on more stable computations.
alg:rays (rays)
Whether to return suffix .unbdd if the objective is unbounded or suffix
.dunbdd if the constraints are infeasible:
0 - Neither
1 - Just .unbdd
2 - Just .dunbdd
3 - Both (default)
alg:relax (relax)
0*/1: Whether to relax integrality of variables.
alg:rhspen (rhspen)
See alg:feasrelax.
alg:sens (sens, solnsens, sensitivity)
Whether to return suffixes for solution sensitivities, i.e., ranges of
values for which the optimal basis remains optimal (note that the
variable and objective values can change):
0 - No (default)
1 - Yes: suffixes returned on variables are
.sensobjlo = smallest objective coefficient
.sensobjhi = greatest objective coefficient
.senslblo = smallest variable lower bound
.senslbhi = greatest variable lower bound
.sensublo = smallest variable upper bound
.sensubhi = greatest variable upper bound;
suffixes for all constraints are
.senslblo = smallest constraint lower bound
.senslbhi = greatest constraint lower bound
.sensublo = smallest constraint upper bound
.sensubhi = greatest constraint upper bound;
suffixes for one-sided constraints only:
.sensrhslo = smallest right-hand side value
.sensrhshi = greatest right-hand side value.
For problems with integer variables or quadratic constraints, alg:sens=0
is assumed quietly.
alg:solutiontarget (solutiontarget)
Specifies the solution targetfor linear programs (LP):
-1 - Automatic (default)
0 - Primal and dual optimal and basic
1 - primal and dual optimal
alg:start (warmstart)
Whether to use incoming primal (and dual, for LP) variable values in a
warmstart:
0 - No
1 - Yes (for LP: if there is no incoming alg:basis) (default)
2 - Yes (for LP: ignoring the incoming alg:basis, if any.)
Note that for LP, "alg:basis" is usually more efficient.
For Gurobi, MIP-specific options can be tuned via "mip:start".
alg:ubpen (ubpen)
See alg:feasrelax.
bar:convtol (barconvtol)
Tolerance on the relative difference between the primal and dual
objectives for stopping the barrier algorithm (default 1e-8).
bar:corr (barcorrectors)
Limit on the number of central corrections done in each barrier
iteration(default -1 = automatic choice).
bar:crossover (crossover)
How to transform a barrier solution to a basic one:
-1 - Automatic choice (default)
0 - None: return an interior solution
1 - Push dual vars first, finish with primal simplex
2 - Push dual vars first, finish with dual simplex
3 - Push primal vars first, finish with primal simplex
4 - Push primal vars first, finish with dual simplex.
bar:crossoverbasis (crossoverbasis)
Strategy for initial basis construction during crossover:
0 - Favor speed (default)
1 - Favor numerical stability.
bar:homog (barhomogeneous)
Whether to use the homogeneous barrier algorithm (e.g., when method=2 is
specified):
-1 - Only when solving a MIP node relaxation (default)
0 - Never
1 - Always.
The homogeneous barrier algorithm can detect infeasibility or
unboundedness directly, without crossover, but is a bit slower than the
nonhomogeneous barrier algorithm.
bar:iterlim (bariterlim)
Limit on the number of barrier iterations (default 1000).
bar:order (barorder)
Ordering used to reduce fill in sparse-matrix factorizations during the
barrier algorithm. Possible values:
-1 - Automatic choice (default)
0 - Approximate minimum degree
1 - Nested dissection.
bar:qcptol (barqcptol)
Convergence tolerance on the relative difference between primal and dual
objective values for barrier algorithms when solving problems with
quadratic constraints (default 1e-6).
cut:agg (cutagg, cut:aggpasses)
Maximum number of constraint aggregation passes during cut generation
(-1 = default = no limit); overrides "cuts".
cut:bqp (bqpcuts)
Whether to enable Boolean Quadric Polytope cut generation:
-1 - Automatic choice (default)
0 - Disallow BQP cuts
1 - Enable moderate BQP cut generation
2 - Enable aggressive BQP cut generation.
Overrides the "cuts" keyword.
cut:clique (cliquecuts)
Overrides "cuts"; choices as for "cuts".
cut:cover (covercuts)
Overrides "cuts"; choices as for "cuts".
cut:cuts (cuts)
Global cut generation control, valid unless overridden by individual
cut-type controls:
-1 - Automatic choice (default)
0 - No cuts
1 - Conservative cut generation
2 - Aggressive cut generation
3 - Very aggressive cut generation.
cut:flowcover (flowcover)
Flowcover cuts: overrides "cuts"; choices as for "cuts".
cut:flowpath (flowpath)
Overrides "cuts"; choices as for "cuts".
cut:gomory (gomory)
Maximum number of Gomory cut passes during cut generation (-1 = default
= no limit); overrides "cuts".
cut:gubcover (gubcover)
Overrides "cuts"; choices as for "cuts".
cut:implied (implied)
Implied cuts: overrides "cuts"; choices as for "cuts".
cut:infproof (infproofcuts)
Whether to generate infeasibility proof cuts:
-1 - Automatic choice (default)
0 - No
1 - Moderate cut generation
2 - Aggressive cut generation.
cut:mipsep (mipsep)
MIPsep cuts: overrides "cuts"; choices as for "cuts".
cut:mir (mircuts)
MIR cuts: overrides "cuts"; choices as for "cuts".
cut:mixingcuts
Mixing cuts: overrides "cuts"
-1 - Automatic choice (default)
0 - No cuts
1 - Conservative cut generation
2 - Aggressive cut generation.
cut:modk (modkcuts)
Mod-k cuts: overrides "cuts"; choices as for "cuts".
cut:network (networkcuts)
Network cuts: overrides "cuts"; choices as for "cuts".
cut:passes (cutpasses)
Maximum number of cutting-plane passes during root-cut generation;
default = -1 ==> automatic choice.
cut:relaxliftcuts (relaxliftcuts)
Whether to enable relax-and-lift cut generation:
-1 - Automatic choice (default)
0 - No cuts
1 - Conservative cut generation
2 - Aggressive cut generation.
cut:rltcuts (rltcuts)
Whether to enable generation of cuts by the Relaxation Linearization
Technique (RLT):
-1 - Automatic choice (default)
0 - No cuts
1 - Conservative cut generation
2 - Aggressive cut generation.
cut:submip (submipcuts)
Sub-MIP cuts: overrides "cuts"; choices as for "cuts".
cut:zerohalf (zerohalfcuts)
Zero-half cuts: overrides "cuts"; choices as for "cuts".
cvt:bigM (cvt:bigm, cvt:mip:bigM, cvt:mip:bigm)
Default value of big-M for linearization of logical constraints. Not
used by default. Use with care (prefer tight bounds). Should be smaller
than (1.0 / [integrality tolerance])
cvt:expcones (expcones)
0*/1: Recognize exponential cones.
cvt:mip:eps (cvt:cmp:eps, cmp:eps)
Tolerance for strict comparison of continuous variables for MIP. Applies
to <, >, and != operators. Also applies to negation of conditional
comparisons: b==1 <==> x<=5 means that with b==0, x>=5+eps. Default:
1e-4.
cvt:names (names, modelnames)
Whether to read or generate variable / constraint / objective names:
0 - No names
1 - (Default) Only provide names if at least one of .col / .row name
files was written by AMPL (AMPL: `option [<solver>_]auxfiles rc;`)
2 - Read names from AMPL, but create generic names if not provided
3 - Create generic names.
cvt:plapprox:domain (plapprox:domain, plapproxdomain)
For piecewise-linear approximated functions, both arguments and result
are bounded to +-[pladomain]. Default 1e6.
cvt:plapprox:reltol (plapprox:reltol, plapproxreltol)
Relative tolerance for piecewise-linear approximation. Default 0.01.
cvt:pre:all
0/1*: Set to 0 to disable most presolve in the flat converter.
cvt:pre:eqbinary
0/1*: Preprocess reified equality comparison with a binary variable.
cvt:pre:eqresult
0/1*: Preprocess reified equality comparison's boolean result bounds.
cvt:pre:unnest
0/1*: Inline nested expressions, currently Ands/Ors.
cvt:quadcon (passquadcon)
0/1*: Multiply out and pass quadratic constraint terms to the solver,
vs. linear approximation.
cvt:quadobj (passquadobj)
0/1*: Multiply out and pass quadratic objective terms to the solver, vs.
linear approximation.
cvt:socp (socpmode, socp)
Second-Order Cone recognition mode:
0 - Do not recognize SOCP forms
1 - Recognize from non-quadratic expressions only (sqrt, abs)
2 - Recognize from quadratic and non-quadratic SOCP forms
Recognized SOCP forms can be further converted to (SOCP-standardized)
quadratic constraints, see cvt:socp2qc. Default: 1.
cvt:socp2qc (socp2qcmode, socp2qc)
Mode to convert recognized SOCP forms to SOCP-standardized quadratic
constraints:
0 - Do not convert
1 - Convert if no other cone types found, and not all original
quadratics could be recognized as SOC, in particular if the
objective is quadratic
2 - Always convert
Such conversion can be necessary if the solver does not accept a mix of
conic and quadratic constraints/objectives. Default: 2.
cvt:sos (sos)
0/1*: Whether to honor declared suffixes .sosno and .ref describing SOS
sets. Each distinct nonzero .sosno value designates an SOS set, of type
1 for positive .sosno values and of type 2 for negative values. The .ref
suffix contains corresponding reference values used to order the
variables.
cvt:sos2 (sos2)
0/1*: Whether to honor SOS2 constraints for nonconvex piecewise-linear
terms, using suffixes .sos and .sosref provided by AMPL.
cvt:uenc:negctx:max (uenc:negctx:max, uenc:negctx)
If cvt:uenc:ratio applies, max number of constants in comparisons
x==const in negative context (equivalently, x!=const in positive
context) to skip UEnc(x). Default 1.
cvt:uenc:ratio (uenc:ratio)
Min ratio (ub-lb)/Nvalues to skip unary encoding for a variable x, where
Nvalues is the number of constants used in conditional comparisons
x==const. Instead, indicator constraints (or big-Ms) are used, if
uenc:negctx also applies. Default 0.
lim:iter (iterlim, iterlimit)
Iteration limit (default: no limit).
lim:mem (memlimit, maxmemoryhard)
Hard limit (number of MB) on memory allocated, causing early termination
if exceeded; default = 0 (no limit)
lim:minrelnodes (minrelnodes)
Number of nodes for the Minimum Relaxation heuristic to explore at the
MIP root node when a feasible solution has not been found by any other
heuristic; default -1 ==> automatic choice.
lim:nodes (nodelim, nodelimit)
Maximum MIP nodes to explore (default: no limit).
lim:softmem (softmemlimit, maxmemorysoft)
Soft limit (number of MB) on memory allocated; default = 0 (no limit)
lim:sol (sollimit, solutionlimit)
Limit the number of feasible MIP solutions found, causing early
termination if exceeded; default = 2e9
lim:startnodes (startnodelimit, startnodes)
Limit on how many branch-and-bound nodes to explore when doing a partial
MIP start:
-3 - Suppress MIP start processing
-2 - Only check full MIP starts for feasibility and ignore partial MIP
starts
-1 - Use "submipnodes" (default)
>=0 - Specific node limit.
lim:submipnodes (submipnodes, maxmipsub)
Limit on nodes explored by MIP-based heuristics, e.g., RINS. Default =
500.
lim:time (timelim, timelimit)
Limit on solve time (in seconds; default: no limit).
lim:work (worklim, worklimit)
Limit on work units. Roughly corresponds to seconds per thread but
deterministic. Default: no limit).
lim:zeroobjnodes (zeroobjnodes)
Number of nodes to explore in the zero objective heuristic. Note that
this heuristic is only applied at the end of the MIP root, and only when
no other root heuristic finds a feasible solution.
This heuristic is quite expensive, and generally produces poor quality
solutions. You should generally only use it if other means, including
exploration of the tree with default settings, fail to produce a
feasible solution.
lp:degenmoves (degenmoves)
Limit on the number of degenerate simplex moves -- for use when too much
time is taken after solving the initial root relaxation of a MIP problem
and before cut generation or root heuristics have started. Default -1
==> automatic choice.
lp:multprice_norm (multprice_norm, normadjust)
Choice of norm used in multiple pricing:
-1 - Automatic choice (default)
0, 1, 2, 3 - Specific choices: hard to describe, but sometimes a
specific choice will perform much better than the automatic choice.
lp:perturb (perturb)
Magnitude of simplex perturbation (when needed; default 2e-4).
lp:pivtol (pivtol, markowitztol)
Markowitz pivot tolerance (default 7.8125e-3).
lp:pricing (pricing)
Pricing strategy:
-1 - Automatic choice (default)
0 - Partial pricing
1 - Steepest edge
2 - Devex
3 - Quick-start steepest edge.
lp:quad (quad)
Whether simplex should use quad-precision:
-1 - Automatic choice (default)
0 - No
1 - Yes.
lp:sifting (sifting)
Whether to use sifting within the dual simplex algorithm, which can be
useful when there are many more variables than constraints:
-1 - Automatic choice (default)
0 - No
1 - Yes, moderate
2 - Yes, aggressive.
lp:siftmethod (siftmethod)
Algorithm to use for sifting with the dual simplex method:
-1 - Automatic choice (default)
0 - Primal simplex
1 - Dual simplex
2 - Barrier.
mip:basis (fixmodel, mip:fix)
Whether to compute duals / basis / sensitivity for MIP models:
0 - No (default)
1 - Yes.
mip:bestbndstop (bestbndstop)
Stop once the best bound on the objective value is at least as good as
this value.
mip:bestbound (bestbound, return_bound)
Whether to return suffix .bestbound for the best known MIP dual bound on
the objective value:
0 - No (default)
1 - Yes.
The suffix is on the objective and problem and is -Infinity for
minimization problems and +Infinity for maximization problems if there
are no integer variables or if a dual bound is not available.
mip:bestobjstop (bestobjstop)
Stop after a feasible solution with objective value at least as good as
this value has been found.
mip:branchdir (branchdir)
Which child node to explore first when branching:
-1 - Explore "down" branch first
0 - Explore "most promising" branch first (default)
1 - Explore "up" branch first.
mip:disconnected (disconnected)
Whether to exploit independent MIP sub-models:
-1 - Automatic choice (default)
0 - No
1 - Moderate effort
2 - Aggressive effort.
mip:fixedmethod (fixedmethod)
Value of "method" to use when seeking a basis for MIP problems when
"mip:basis=1". Default: if "method" is 0 or 1 then "method" else 1.
mip:focus (mipfocus)
MIP solution strategy:
0 - Balance finding good feasible solutions and proving optimality
(default)
1 - Favor finding feasible solutions
2 - Favor providing optimality
3 - Focus on improving the best objective bound.
mip:gap (mipgap)
Max. relative MIP optimality gap (default 1e-4).
mip:gapabs (mipgapabs)
Max. absolute MIP optimality gap (default 1e-10).
mip:heurfrac (heurfrac)
Fraction of time to spend in MIP heuristics (default 0.05).
mip:improvegap (improvegap)
Optimality gap below which the MIP solver switches from trying to
improve the best bound to trying to find better feasible solutions
(default 0).
mip:improvetime (improvetime)
Execution seconds after which the MIP solver switches from trying to
improve the best bound to trying to find better feasible solutions
(default Infinity).
mip:impstartnodes (impstartnodes)
Number of MIP nodes after which the solution strategy will change from
improving the best bound to finding better feasible solutions (default
Infinity).
mip:intfocus (integralityfocus, intfocus)
Setting this parameter to 1 requests the solver to work harder at
finding solutions that are still (nearly) feasible when all integer
variables are rounded to exact integral values to avoid numerical issues
such as trickle flow:
0 - No (default)
1 - Yes.
mip:inttol (inttol, intfeastol)
Feasibility tolerance for integer variables (default 1e-05).
mip:lazy (lazy)
Whether to recognize suffix .lazy on constraints: sum of
1 - Accept .lazy>0 values (true lazy constraints, if supported)
2 - Accept .lazy<0 values (user cuts, if supported)
Default lazy = 3 ==> accept both.
For Gurobi, lazy/user constraints are indicated with .lazy values of -1,
1, 2, or 3 and are ignored until a solution feasible to the remaining
constraints is found. What happens next depends on the value of .lazy:
-1 - Treat the constraint as a user cut; the constraint must be
redundant with respect to the rest of the model, although it can cut off
LP solutions;
1 - The constraint may still be ignored if another lazy constraint cuts
off the current solution;
2 - The constraint will henceforth be enforced if it is violated by the
current solution;
3 - The constraint will henceforth be enforced.
mip:nodemethod (nodemethod)
Algorithm used to solve relaxed MIP node problems:
-1 - Automatic choice (default)
0 - Primal simplex
1 - Dual simplex
2 - Barrier.
mip:norelheurtime (norelheurtime)
Limits the amount of time (in seconds) spent in the NoRel heuristic; see
the description of "norelheurwork" for details. This parameter will
introduce nondeterminism; use "norelheurwork" for deterministic results.
Default 0.
mip:norelheurwork (norelheurwork)
Limits the amount of work spent in the NoRel heuristic. This heuristic
searches for high-quality feasible solutions before solving the root
relaxation. The work metrix is hard to define precisely, as it depends
on the machine. Default 0.
mip:obbt (obbt)
Controls aggressiveness of Optimality - Based Bound Tightening:
-1 - Automatic choice (default)
0 - No
1 - Yes
2 - Yes, more aggressively
3 - Yes, even more aggressively.
mip:opttol (opttol, optimalitytolerance)
Dual feasibility tolerance.
mip:partition (partitionplace)
Whether and how to use the .partition suffix on variables in the
partition heuristic for MIP problems: sum of
1 ==> When the branch-and-cut search ends
2 ==> At nodes in the branch-and-cut search
4 ==> After the root-cut loop
8 ==> At the start of the root-cut loop
16 ==> Before solving the root relaxation.
Default = 15. Values of .parition determine how variables participate in
the partition heuristic. Variables with
.partition = -1 are always held fixed;
.partition = 0 can vary in all sub-MIP models;
.partition > 0 can vary only in in that sub-MIP model.
The partition heuristic is only run when partition_place is between 1
and 31 and some variables have suitable .partition suffix values.
mip:priorities (priorities)
0/1*: Whether to read the branch and bound priorities from the .priority
suffix.
mip:pumppasses (pumppasses)
Number of feasibility-pump passes to do after the MIP root when no other
root heuristoc found a feasible solution. Default -1 = automatic choice.
mip:return_gap (return_mipgap)
Whether to return mipgap suffixes or include mipgap values (|objectve -
.bestbound|) in the solve_message: sum of
1 - Return .relmipgap suffix (relative to |obj|)
2 - Return .absmipgap suffix (absolute mipgap)
4 - Suppress mipgap values in solve_message.
Default = 0. The suffixes are on the objective and problem. Returned
suffix values are +Infinity if no integer-feasible solution has been
found, in which case no mipgap values are reported in the solve_message.
mip:rins (rins)
How often to apply the RINS heuristic for MIP problems:
-1 - Automatic choice (default)
0 - never
n > 0 - every n-th node.
mip:round (round)
Whether to round integer variables to integral values before returning
the solution, and whether to report that the solver returned noninteger
values for integer values: sum of
1 ==> Round nonintegral integer variables
2 ==> Modify solve_result
4 ==> Modify solve_message
Default = 0. Modifications that were or would be made are reported in
solve_result and solve_message only if the maximum deviation from
integrality exceeded mip:round_reptol.
With Gurobi, for problems with numerical issues such as trickle flow,
option "mip:intfocus" can be more reliable.
mip:round_reptol (round_reptol)
Tolerance for reporting rounding of integer variables to integer values;
see "mip:round". Default = 1e-9.
mip:start (mipstart, intstart)
Whether to use initial guesses in problems with integer variables:
0 - No (overrides alg:start)
1 - Yes (default)
2 - No, but use the incoming primal values as hints (VARHINTVAL),
ignoring the .hintpri suffix
3 - Similar to 2, but use the .hintpri suffix on variables: larger
(integer) values give greater priority to the initial value of the
associated variable.
mip:symmetry (symmetry)
MIP symmetry detection:
-1 - Automatic choice (default)
0 - No
1 - Conservative
2 - Aggressive.
mip:varbranch (varbranch)
MIP branch variable selection strategy:
-1 - Automatic choice (default)
0 - Pseudo reduced - cost branching
1 - Pseudo shadow - price branching
2 - Maximum infeasibility branching
3 - Strong branching.
miqcp:method (miqcpmethod)
Method for solving mixed-integer quadratically constrained (MIQCP)
problems:
-1 - Automatic choice (default)
0 - Solve continuous QCP relaxations at each node
1 - Use linearized outer approximations.
obj:*:abstol (obj_*_abstol)
Absolute tolerance for objective with index *. Can only be applied on a
multi-objective problem with obj:multi=1
obj:*:method (obj_*_method)
Method for objective with index *
obj:*:priority (obj_*_priority)
Priority for objective with index *
obj:*:reltol (obj_*_reltol)
Relative tolerance for objective with index *
obj:*:weight (obj_*_weight)
Weight for objective with index *
obj:multi (multiobj)
0*/1: Whether to do multi-objective optimization.
When obj:multi = 1 and several objectives are present, suffixes
.objpriority, .objweight, .objreltol, and .objabstol on the objectives
are relevant. Objectives with greater .objpriority values (integer
values) have higher priority. Objectives with the same .objpriority are
weighted by .objweight. Objectives with positive .objabstol or
.objreltol are allowed to be degraded by lower priority objectives by
amounts not exceeding the .objabstol (absolute) and .objreltol
(relative) limits. The objectives must all be linear. Objective-specific
convergence tolerances and method values may be assigned via keywords of
the form obj_n_<name>, such as obj_1_method for the first objective.
obj:multiobjmethod (multiobjmethod)
Choice of optimization algorithm for lower-priority objectives:
-1 - Automatic choice (default)
0 - Primal simplex
1 - Dual simplex
2 - Ignore warm-start information; use the algorithm specified by the
method keyword.
The method keyword determines the algorithm to use for the highest
priority objective.
obj:multiobjpre (multiobjpre)
How to apply Gurobi's presolve when doing multi-objective optimization:
-1 - Automatic choice (default)
0 - Do not use Gurobi's presolve
1 - Conservative presolve
2 - Aggressive presolve, which may degrade lower priority objectives.
obj:no (objno)
Objective to optimize:
0 - None
1 - First (default, if available)
2 - Second (if available), etc.
obj:scale (objscale)
How to scale the objective:
0 - Automatic choice (default)
-1..0 - Divide by max abs. coefficient raised to this power
>0 - Divide by this value.
pre:aggfill (aggfill)
Amount of fill allowed during aggregation in presolve(default -1).
pre:aggregate (aggregate)
0/1*: whether to use aggregation in presolve.Setting it to 0 can
sometimes reduce numerical errors.
pre:deprow (predeprow)
Whether Gurobi's presolve should remove linearly dependent
constraint-matrix rows:
-1 - Only for continuous models (default)
0 - Never
1 - For all models.
pre:dual (predual)
Whether Gurobi's presolve should form the dual of a continuous model:
-1 - Automatic choice (default)
0 - No
1 - Yes
2 - Form both primal and dual and use two threads to choose
heuristically between them.
pre:dualreductions (dualreductions)
Whether Gurobi's presolve should use dual reductions, which may be
useful on a well-posed problem but can prevent distinguishing whether a
problem is infeasible or unbounded:
0 - No
1 - Yes (default)
pre:funcnonlinear (funcnonlinear, global)
Controls how general functions with their constraint's or objective's
suffix .funcnonlinear or, if not available, .global unset (or set to 0)
are treated (ATTENTION: different meaning than Gurobi FuncNonLinear
parameter and attribute):
-1 - Piecewise-linear approximation
0 - Automatic (default)
1 - Treated as nonlinear functions
Suffix values mean the same.
pre:funcpieceerror (funcpieceerror)
For 'funcpieces=-1' or -2, this option provides the maximum allowed
error (absolute for -1, relative for -2) in the piecewise-linear
approximation.
The value can be overridden by suffix .funcpieceerror of the individual
constraints.
pre:funcpiecelength (funcpiecelength)
If 'funcpieces=1', this option or suffix provide the length of each
piece of the piecewise-linear approximation.
pre:funcpieceratio (funcpieceratio)
This option (and suffix) control whether the piecewise-linear
approximation of a function constraint is an underestimate of the
function, an overestimate, or somewhere in between. A value of 0.0 will
always underestimate, while a value of 1.0 will always overestimate. A
value in between will interpolate between the underestimate and the
overestimate. A special value of -1 chooses points that are on the
original function.
pre:funcpieces (funcpieces)
This option (and suffix) set the strategy used for performing a
piecewise-linear approximation of a function constraint. They have the
following meaning:
0 - Automatic choice (default)
>=2 - Sets the number of pieces; pieces are equal width
1 - Uses a fixed width for each piece; the actual width is provided in
the 'funcpiecelength' option/suffix
-1 - Bounds the absolute error of the approximation; the error bound is
provided in the 'funcpieceerror' option/suffix
-2 - Bounds the relative error of the approximation; the error bound is
provided in the 'funcpieceerror' option/suffix.
pre:funcpiecesuf (funcpiecesuf, funcpiecesuffixes)
0/1*: whether to consider the individual .funcpiece... suffixes in
objectives and constraints, which impact Gurobi's approximation quality
of nonlinear constraints, beyond the corresponding global options
pre:miqcpform (premiqcpform)
For mixed-integer quadratically constrained (MIQCP) problems, how Gurobi
should transform quadratic constraints:
-1 - Automatic choice (default)
0 - Retain MIQCP form
1 - Transform to second-order cone contraints
2 - Transform to rotated cone constraints.
Choices 0 and 1 work with general quadratic constraints. Choices 1 and 2
only work with constraints of suitable forms.
pre:passes (prepasses)
Limit on the number of Gurobi presolve passes:
-1 - Automatic choice (default)
n>=0 - At most n passes.
pre:qlinearize (preqlinearize, preqlin)
How Gurobi's presolve should treat quadratic problems:
-1 - Automatic choice (default)
0 - Do not modify the quadratic part(s)
1 or 2 = try to linearize quadratic parts:
1 - Focus on a strong LP relaxation
2 - Focus on a compact LP relaxation.
pre:scale (scale)
Whether to scale the problem:
-1 - Automatic choice (default)
0 - No
1 - Yes
2 - Yes, more aggressively
3 - Yes, even more aggressively.
Scaling typically reduces solution times, but it may lead to larger
constraint violations in the original, unscaled model. Choosing a
different scaling option can sometimes improve performance for
particularly numerically difficult models.
pre:solve (presolve)
Whether to use Gurobi's presolve:
-1 - Automatic choice (default)
0 - No
1 - Conservative
2 - Aggressive.
pre:sos1bigm (presos1bigm)
Big-M for converting SOS1 constraints to binary form:
-1 - Automatic choice (default)
0 - No conversion
Large values (e.g., 1e8) may cause numeric trouble.
pre:sos1enc (presos1enc)
Encoding used for SOS1 reformulation:
-1 - Automatic choice (default)
0 - Multiple choice model, produces an LP relaxation that is easy to
solve
1 - Incremental model, reduces the amount of branching
2 - Formulation whose LP relaxation is easier to solve
3 - Formulation with better branching behavior, requires sum of the
variables == 1.
Options 0 and 1 produce reformulations that are linear in size; options
2 and 3 use reformulation logarithmic in size. Option 2 and 3 apply only
when all the variables are >=0.
pre:sos2bigm (presos2bigm)
Big-M for converting SOS2 constraints to binary form:
-1 - Automatic choice (default)
0 - No conversion
Large values (e.g., 1e8) may cause numeric trouble.
pre:sos2enc (presos2enc)
Encoding used for SOS2 reformulation, see presos1enc.
pre:sparsify (presparsify)
Whether Gurobi's presolve should use its "sparsify reduction", which
sometimes gives significant problem-size reductions:
-1 - Automatic choice (default)
0 - No
1 - Yes.
qcp:dual (qcpdual)
Whether to compute dual variables when the problem has quadratic
constraints (which can be expensive):
0 - No (default)
1 - Yes.
qp:nonconvex (nonconvex)
How to handle non-convex quadratic objectives and constraints:
-1 - Default choice (currently almost the same as 2)
0 - Complain about nonquadratic terms
1 - Complain if Gurobi's presolve cannot discard or eliminate
nonquadratic terms
2 - Translate quadratic forms to bilinear form and use spatial
branching.
qp:psdtol (psdtol)
Maximum diagonal perturbation to correct indefiniteness in quadratic
objectives (default 1e-6).
sol:chk:fail (chk:fail, checkfail)
Fail on MP solution check violations, with solve result 150.
sol:chk:feastol (sol:chk:eps, chk:eps, chk:feastol)
Absolute tolerance to check objective values, variable and constraint
bounds. Default 1e-6.
sol:chk:feastolrel (sol:chk:epsrel, chk:epsrel, chk:feastolrel)
Relative tolerance to check objective values, variable and constraint
bounds. Default 1e-6.
sol:chk:infeas (chk:infeas, checkinfeas)
Check even infeasible solution condidates, whenever solver reports them.
sol:chk:inttol (sol:chk:inteps, sol:inteps, chk:inttol)
Solution checking tolerance for variables' integrality. Default 1e-5.
sol:chk:mode (solcheck, checkmode, chk:mode)
Solution checking mode. Sum of a subset of the following bits:
1 - Check variable bounds and integrality.
2 - Check original model constraints, as well as any non-linear
expression values reported by the solver.
4 - Check intermediate auxiliary constraints (i.e., those which were
reformulated further).
8 - Check final auxiliary constraints sent to solver.
16 - Check objective values.
32, 64, 128, 256, 512 - similar, but non-linear expressions are
recomputed (vs using their values reported by the solver.)
*Experimental.* This is an idealistic check, because it does not
consider possible tolerances applied by the solver when computing
expression values.
Default: 1+2+512.
sol:chk:prec (chk:prec, chk:precision)
AMPL solution_precision option when checking: number of significant
digits.
sol:chk:round (chk:round, chk:rnd)
AMPL solution_round option when checking: round to this number of
decimals after comma (before comma if negative.)
sol:count (countsolutions)
0*/1: Whether to count the number of solutions and return it in the
".nsol" problem suffix. The number and kind of solutions are controlled
by the sol:pool... parameters. Value 1 implied by sol:stub.
sol:poolgap (ams_eps, poolgap)
Relative tolerance for reporting alternate MIP solutions (default:
Infinity, no limit).
sol:poolgapabs (ams_epsabs, poolgapabs)
Absolute tolerance for reporting alternate MIP solutions (default:
Infinity, no limit).
sol:poollimit (ams_limit, poollimit, solnlimit)
Limit on the number of alternate MIP solutions written. Default: 10.
sol:poolmode (ams_mode, poolmode)
Search mode for MIP solutions when sol:stub/sol:count are specified to
request finding several alternative solutions:
0 - Just collect solutions during normal solve, and sort them
best-first
1 - Make some effort at finding additional solutions
2 - Seek "poollimit" best solutions (default).'Best solutions' are
defined by the poolgap(abs) parameters.
sol:stub (ams_stub, solstub, solutionstub)
Stub for alternative MIP solutions, written to files with names obtained
by appending "1.sol", "2.sol", etc., to <solutionstub>. The number of
such files written is affected by the keywords poolgap, poolgapabs,
poollimit, and poolmode. The number of alternative MIP solution files
written is returned in suffix .nsol on the problem.
tech:cloudid (cloudid)
Use Gurobi Instant Cloud with this "accessID".
tech:cloudkey (cloudkey)
Use Gurobi Instant Cloud with this "secretKey". Both cloudid and
cloudkey are required.
tech:cloudpool (cloudpool)
Optional "machine pool" to use with Gurobi Instant Cloud.
tech:cloudpriority (cloudpriority)
Priority of Cloud job, an integer >= -100 and <= 100. Default 0. Jobs
with priority 100 run immediately -- use caution when specifying this
value.
tech:concurrentmip (concurrentmip)
How many independent MIP solves to allow at once when multiple threads
are available. Optimization terminates when the first solve completes.
The available threads are divided as evenly as possible among the
concurrent solves. Default = 1.
See also "tech:distmip", "tech:pooljobs".
tech:debug (debug)
0*/1: whether to assist testing & debugging, e.g., by outputting
auxiliary information.
tech:distmip (pool_distmip, distmip)
Enables distributed MIP. A value of n causes the MIP solver to divide
the work of solving a MIP model among n machines. Use the "tech:server"
parameter to indicate the name of the cluster where you would like your
distributed MIP job to run (or use "tech:workerpool" if your client
machine will act as manager and you just need a pool of workers).
Default = 0.
See also "tech:concurrentmip", "tech:pooljobs".
tech:logfile (logfile)
Log file name; note that the solver log will be written to the log
regardless of the value of tech:outlev.
tech:logfreq (logfreq, outfreq)
Interval in seconds between log lines (default 5).
tech:nodefiledir (nodefiledir)
Directory where MIP tree nodes are written after memory for them exceeds
"nodefilestart"; default "."
tech:nodefilestart (nodefilestart)
Gigabytes of memory to use for MIP tree nodes; default = Infinity (no
limit, i.e., no node files written).
tech:optionfile (optionfile, option:file)
Name of an AMPL solver option file to read (surrounded by 'single' or
"double" quotes if the name contains blanks). Lines that start with #
are ignored. Otherwise, each nonempty line should contain "name=value",
e.g., "lim:iter=500".
tech:optionnative (optionnative, optnative, tech:param)
General way to specify values of both documented and undocumented Gurobi
parameters; value should be a quoted string (delimited by ' or ")
containing a parameter name, a space, and the value to be assigned to
the parameter. Can appear more than once. Cannot be used to query
current parameter values.
tech:optionnativeread (optionnativeread, tech:param:read, param:read)
Name of Gurobi parameter file (surrounded by 'single' or "double" quotes
if the name contains blanks). The suffix on a parameter file should be
.prm, optionally followed by .zip, .gz, .bz2, or .7z.
Lines that start with # are ignored. Otherwise, each nonempty line
should contain a name and a value, separated by a space.
tech:optionnativewrite (optionnativewrite, tech:param:write, param:write)
Name of Gurobi parameter file (surrounded by 'single' or "double" quotes
if the name contains blanks) to be written.
tech:outlev (outlev)
0*/1: Whether to write gurobi log lines (chatter) to stdout.
tech:pooljobs (pool_jobs, pooljobs)
Enables distributed concurrent optimization, which can be used to solve
LP or MIP models on multiple machines. A value of n causes the solver to
create n independent models, using different parameter settings for
each. Each of these models is sent to a distributed worker for
processing. Optimization terminates when the first solve completes. Use
the "tech:server" parameter to indicate the name of the cluster where
you would like your distributed concurrent job to run (or use
"tech:workerpool" if your client machine will act as manager and you
just need a pool of workers). Default = 0.
See also "tech:concurrentmip", "tech:distmip".
tech:resultfile (resultfile)
Name of a file of extra information written after completion of
optimization. The name's suffix determines what is written:
.sol - Solution vector
.bas - Simplex basis
.mst - Integer variable solution vector
.ilp - IIS for an infeasible model
.mps, .rew, .lp, or .rlp - To capture the original model.
The file suffix may optionally be followed by .gz, .bz2, or .7z, which
produces a compressed result. Use tech:writesolution to write several
files.
tech:seed (seed)
Random number seed (default 0), affecting perturbations that may
influence the solution path.
tech:server (server, servers)
Comma-separated list of Gurobi Compute Servers, specified either by name
or by IP address. Default: run Gurobi locally (i.e., do not use a remote
Gurobi server).
tech:server_group (server_group)
Name of Compute Server Group, if any.
tech:server_insecure (server_insecure)
Whether to user "insecure mode" with the Gurobi Compute Server. Should
be left at default value (0) unless an administrator specifies another
value.
tech:server_lic (serverlic, server_lic)
Synonym for tech:optionfile.
tech:server_password (server_password)
Password (if needed) for specified Gurobi Compute Server(s).
tech:server_priority (server_priority)
Priority for Gurobi Compute Server(s). Default = 0. Highest priority =
100.
tech:server_router (server_router)
Name or IP address of router for Compute Server, if any.
tech:server_timeout (server_timeout)
Report job as rejected by Gurobi Compute Server if the job is not
started within server_timeout seconds. Default = 10.
tech:threads (threads)
How many threads to use when using the barrier algorithm or solving MIP
problems; default 0 ==> automatic choice.
tech:timing (timing)
0*/1: Whether to display timings for the run.
tech:tunebase (tunebase)
Base name for results of running Gurobi's search for best parameter
settings. The search is run only when tunebase is specified. Results are
written to files with names derived from tunebase by appending ".prm" if
".prm" does not occur in tunebase and inserting _1_, _2_, ... (for the
first, second, ... set of parameter settings) before the right-most
".prm". The file with _1_ inserted is the best set and the solve results
returned are for this set. In a subsequent "solve;", you can use
"tech:param:read=..." to apply the settings in results file ... .
tech:tunedynamicjobs (pool_tunedynamicjobs, tunedynamicjobs)
Enables distributed parallel tuning, which can significantly increase
the performance of the tuning tool. A value of n causes the tuning tool
to use a dynamic set of up to n workers in parallel. A value of -1
allows the solver to use an unlimited number of workers. Default = 0.
tech:tunejobs (pool_tunejobs, tunejobs)
Enables distributed parallel tuning, which can significantly increase
the performance of the tuning tool. A value of n causes the tuning tool
to distribute tuning work among n parallel jobs. These jobs are
distributed among a set of machines. Use the "tech:workerpool" parameter
to provide a distributed worker cluster. Default = 0.
Note that distributed tuning is most effective when the worker machines
have similar performance.
tech:tuneoutput (tuneoutput)
Amount of tuning output when tunebase is specified:
0 - None
1 - Summarize each new best parameter set
2 - Summarize each set tried (default)
3 - Summary plus detailed solver output for each trial.
tech:tuneresults (tuneresults)
Limit on the number of tuning result files to write when tunerbase is
specified. The default (-1) is to write results for all parameter sets
on the efficient frontier.
tech:tunetimelim (tunetimelim, lim:tunetime)
Time limit (in seconds) on tuning when tunebase is specified. Default -1
==> automatic choice of time limit.
tech:tunetrials (tunetrials)
Number of trials for each parameter set when tunebase is specified, each
with a different random seed value. Default = 3.
tech:version (version)
Single-word phrase: report version details before solving the problem.
tech:wantsol (wantsol)
In a stand-alone invocation (no "-AMPL" on the command line), what
solution information to write. Sum of
1 - Write ".sol" file
2 - Primal variables to stdout
4 - Dual variables to stdout
8 - Suppress solution message.
tech:workerpassword (pool_password)
Password for the worker pool (if needed).
tech:workerpool (pool_servers)
When using a distributed algorithm (distributed MIP, distributed
concurrent, or distributed tuning), this parameter allows you to specify
a Remote Services cluster that will provide distributed workers. You
should also specify the access password for that cluster, if there is
one, in the "workerpassword" parameter. Note that you don't need to set
either of these parameters if your job is running on a Compute Server
node and you want to use the same cluster for the distributed workers.
You can provide a comma-separated list of machines for added robustness.
tech:writegraph (writegraph, exportgraph)
File to export conversion graph. Format: JSON Lines.
tech:writemodel (writeprob, writemodel, tech:exportfile)
Specifies files where to export the model before solving (repeat the
option for several files.) File name extensions can be ".lp[.7z]",
".mps", etc.
tech:writemodelonly (justwriteprob, justwritemodel)
Specifies files where to export the model, no solving (option can be
repeated.) File extensions can be ".dlp", ".mps", etc.
tech:writepresolved (writepresolved, writepresolvedmodel, exportpresolvedfile)
Specifies the name of a file where to export the presolved model before
solving it. This file name can have extension ".lp", ".mps", etc.
Default = "" (don't export the model).
tech:writesolution (writesol, writesolution)
Specifies the names of files where to export the solution and/or other
result files in solver's native formats. Option can be repeated. File
name extensions can be ".sol[.tar.gz]", ".json", ".bas", ".ilp", etc.
```