Obtaining information
In addition to the Knitro log that is printed on screen, information about the computation performed by Knitro is available in the form of various function calls. This section explains how this information can be retrieved and interpreted.
Knitro output for continuous problems
This section describes Knitro outputs at various levels
for continuous problems. We examine the output that results from running
examples/C/exampleNLP1.c with full output.
Note
If outlev=0 then all printing of output is suppressed.
If outlev is positive, then Knitro prints
information about the solution of your optimization problem either to
standard output (outmode = screen), to a file named
knitro.log (outmode = file), or to
both (outmode = both).
The option outdir controls the directory where output files are
created (if any are) and the option outappend controls whether
output is appended to existing files.
Display of Nondefault Options
Knitro first prints the banner displaying the Artelys license type
and version of Knitro that is installed.
It then lists all user options which are different from their default values
If nothing is listed in this section then it must be that all user options
are set to their default values.
Lastly, Knitro prints messages that describe how it resolved user
options that were set to automatic values.
For example, if option algorithm = auto, then Knitro
prints the algorithm that it chooses.
=======================================
Commercial License
Artelys Knitro 14.1.0
=======================================
Knitro presolve eliminated 0 variables and 0 constraints.
outlev: 6
Knitro changing algorithm from AUTO to 1.
Knitro changing bar_initpt from AUTO to 3.
Knitro changing bar_murule from AUTO to 4.
Knitro changing bar_penaltycons from AUTO to 1.
Knitro changing bar_penaltyrule from AUTO to 2.
Knitro changing bar_switchrule from AUTO to 2.
Knitro changing linesearch from AUTO to 1.
Knitro changing linsolver from AUTO to 2.
In the example above, it is indicated that we are using a more verbose
output level (outlev = 6) instead of the default value
(outlev = 2).
Knitro chose algorithm 1 (Interior/Direct), and then automatically
determined some other options related to the algorithm.
Display of problem characteristics
Knitro next prints a summary description of the problem characteristics including the number and type of variables and constraints and the number of nonzero elements in the Jacobian matrix and Hessian matrix. If the Knitro presolver is enabled, then information about the presolved form of the problem is printed as well.
Problem Characteristics ( Presolved)
-----------------------
Objective goal: Minimize
Objective type: general
Number of variables: 2 ( 2)
bounded below only: 0 ( 0)
bounded above only: 1 ( 1)
bounded below and above: 0 ( 0)
fixed: 0 ( 0)
free: 1 ( 1)
Number of constraints: 2 ( 2)
linear equalities: 0 ( 0)
quadratic equalities: 0 ( 0)
gen. nonlinear equalities: 0 ( 0)
linear one-sided inequalities: 0 ( 0)
quadratic one-sided inequalities: 2 ( 2)
gen. nonlinear one-sided inequalities: 0 ( 0)
linear two-sided inequalities: 0 ( 0)
quadratic two-sided inequalities: 0 ( 0)
gen. nonlinear two-sided inequalities: 0 ( 0)
Number of nonzeros in Jacobian: 4 ( 4)
Number of nonzeros in Hessian: 3 ( 3)
Display of Iteration Information
Next, if outlev is greater than 2, Knitro prints
columns of data reflecting detailed information about individual
iterations during the solution process.
An iteration is defined as a step
which generates a new solution estimate (i.e., a successful step).
If outlev = 2, summary data is printed every 10
iterations, and on the final iteration. If
outlev = 3, summary data is printed every
iteration. If outlev = 4, the most verbose
iteration information is printed every iteration.
Iter fCount Objective FeasError OptError ||Step|| CGits
-------- -------- -------------- ---------- ---------- ---------- -------
0 7 9.090000e+02 3.000e+00
1 8 7.996681e+02 2.859e+00 2.186e+01 7.226e-02 0
2 9 1.859212e+01 9.066e-01 3.943e+01 2.199e+00 0
3 17 3.280079e+02 8.816e-01 6.903e+00 1.356e+00 8
4 18 1.445972e+01 4.912e-01 6.736e-01 1.173e+00 2
5 19 3.562070e+01 3.874e-01 3.874e-01 1.929e-01 0
6 20 1.153310e+02 2.196e-01 5.652e-01 4.098e-01 0
7 21 2.363651e+02 7.226e-02 7.226e-02 4.156e-01 0
8 22 3.018949e+02 5.268e-03 1.827e-02 1.861e-01 0
9 23 3.064952e+02 6.791e-06 1.513e-04 1.267e-02 0
10 24 3.065000e+02 9.480e-11 9.480e-11 1.358e-05 0
The meaning of each column is described below.
Iter: iteration number.
fCount: the cumulative number of (nonlinear) function evalutions. (This information is only printed if
outlevis greater than 3).Objective: the value of the objective function at the current iterate.
FeasError: a measure of the feasibility violation at the current iterate
OptError: a measure of the violation of the Karush-Kuhn-Tucker (KKT) (first-order) optimality conditions (not including feasibility) at the current iterate.
Step: the 2-norm length of the step (i.e., the distance between the new iterate and the previous iterate).
CGits: the number of Projected Conjugate Gradient (CG) iterations required to compute the step.
Display of termination status
At the end of the run a termination message is printed indicating whether or not the optimal solution was found and if not, why Knitro stopped. The termination message typically starts with the word “EXIT”. If Knitro was successful in satisfying the termination test, the message will look as follows:
EXIT: Locally optimal solution found.
Display of Final Statistics
Following the termination message, a summary of some final statistics on the run are printed. Both relative and absolute error values are printed.
Final Statistics
----------------
Final objective value = 3.06499999937285e+02
Final feasibility error (abs / rel) = 9.48e-11 / 3.16e-11
Final optimality error (abs / rel) = 9.48e-11 / 6.50e-12
# of iterations = 10
# of CG iterations = 10
# of function evaluations = 24
# of gradient evaluations = 15
# of Hessian evaluations = 10
Total program time (secs) = 0.00258 ( 0.002 CPU time)
Time spent in evaluations (secs) = 0.00002
Display of solution vector and constraints
If outlev equals 5 or 6, the values of the solution vector are printed
after the final statistics. If outlev equals 6, the final constraint
values are also printed, and the values of the
Lagrange multipliers (or dual variables) are printed next to their corresponding
constraint or bound.
Constraint Vector Lagrange Multipliers
----------------- ---------------------
c[ 0] = 9.99999999905e-01, lambda[ 0] = -6.99999999925e+02
c[ 1] = 4.49999999927e+00, lambda[ 1] = -8.09211653221e-10
Solution Vector
---------------
x[ 0] = 4.99999999998e-01, lambda[ 2] = 1.75099999969e+03
x[ 1] = 1.99999999982e+00, lambda[ 3] = 0.00000000000e+00
Debugging / profiling information
Knitro can produce
additional information which may be useful in debugging or analyzing
performance. If outlev is positive and
debug = 1, then multiple files named kdbg_*.log are
created which contain detailed information on performance.
If outlev is positive and debug = 2,
then Knitro prints information useful for debugging program execution.
The information produced by debug
is primarily intended for developers, and should not be
used in a production setting.
Intermediate iterates
Users can generate a file containing iterates and/or solution points
with option newpoint. The output file is called
knitro_newpoint.log.
Knitro output for discrete problems
This section describes Knitro outputs at various levels
for discrete or mixed integer problems. We examine the output
that results from running examples/C/callbackMINLP1.c.
Note
When outlev is positive, the options mip_outlevel,
mip_debug, mip_outinterval and
mip_outsub control the
amount and type of MIP output generated as described below.
Knitro first prints the banner displaying the license type
and version of Knitro that is installed.
It then lists all user options which are different from their default values.
If nothing is listed in this section then it must be that all user options
are set to their default values.
Lastly, Knitro prints messages that describe how it resolved user
options that were set to automatic values. For example, if
option mip_branchrule = auto,
then Knitro prints the branching rule that it chooses.
=======================================
Commercial License
Artelys Knitro 14.1.0
=======================================
No start point provided -- Knitro computing one.
mip_method: 1
mip_outinterval: 1
Knitro changing mip_rootalg from AUTO to 1.
Knitro changing mip_lpalg from AUTO to 3.
Knitro changing mip_branchrule from AUTO to 2.
Knitro changing mip_selectrule from AUTO to 2.
Knitro changing mip_rounding from AUTO to 3.
Knitro changing mip_pseudoinit from AUTO to 1.
In the example above, it is indicated that we are using
mip_method = 1 which is the standard branch-and-bound method,
and that we are printing output
information at every node since mip_outinterval = 1.
It then determined seven other options related to the MIP method.
If no initial point is provided by the user, Knitro indicates
that it is computing one.
Display of Problem Characteristics
Knitro next prints a summary description of the problem characteristics including the number and type of variables and constraints and the number of nonzero elements in the Jacobian matrix and Hessian matrix (if providing the exact Hessian). Knitro also prints the results of any MIP preprocessing to detect special structure.
Problem Characteristics
-----------------------
Objective goal: Minimize
Objective type: general
Number of variables: 6
bounded below only: 0
bounded above only: 0
bounded below and above: 6
fixed: 0
free: 0
Number of binary variables: 3
Number of integer variables: 0
Number of constraints: 6
linear equalities: 0
quadratic equalities: 0
gen. nonlinear equalities: 0
linear one-sided inequalities: 4
quadratic one-sided inequalities: 0
gen. nonlinear one-sided inequalities: 2
linear two-sided inequalities: 0
quadratic two-sided inequalities: 0
gen. nonlinear two-sided inequalities: 0
Number of nonzeros in Jacobian: 16
Number of nonzeros in Hessian: 3
Knitro detected 1 GUB constraint
Knitro derived 0 knapsack covers after examining 3 constraints
Display of Node Information
Next, if mip_outlevel = 1, Knitro prints
columns of data reflecting detailed information about individual
nodes during the solution process.
If mip_outlevel = 2, the accumulated time is printed at
each node also.
The frequency of this node
information is controlled by the mip_outinterval parameter.
For example, if mip_outinterval = 100, this node information
is printed only for every 100th node (printing output less
frequently may save significant CPU time in some cases). In the example
below, mip_outinterval = 1, so information about every node is
printed (without the accumulated time).
Nodes Best solution Bound Gap
Expl | Unexpl value
0 1 0.759284
0 1 0.759284
0 1 10.0000 FP 0.759284 92.41%
1 2 10.0000 0.759284 92.41%
1 2 10.0000 0.759284 92.41%
2 1 6.00976 LEAF 0.759284 87.37%
3 2 6.00976 5.17132 13.95%
3 2 6.00976 5.17132 13.95%
5 0 6.00976 6.00976 0.00%
The meaning of each column is described below.
Node: indicates the node number (Expl) and the current number of active nodes left in the branch-and-bound tree (Unexpl).
Best solution value: the value of the current best relaxation (lower bound on the solution if minimizing).
Bound: the value of the current best integer feasible point (upper bound on the solution if minimizing).
Gap: the gap between the best relaxation and the best feasible (incumbent) solution expressed as a percentage.
Display of Termination Status
At the end of the run a termination message is printed indicating whether or not the optimal solution was found and if not, why Knitro stopped. The termination message typically starts with the word “EXIT”. If Knitro was successful in satisfying the termination test, the message will look as follows:
EXIT: Optimal solution found (assuming convexity).
See the reference manual (Return codes) for a list of possible termination
messages and a description of their meaning and the corresponding
value returned by KN_solve().
Display of Final Statistics
Following the termination message, a summary of some final statistics on the run are printed, as well as some statistics related to cuts and heuristics.
Final Statistics for MIP
------------------------
Final objective value = 6.00975890892825e+00
Final bound value = 6.00975890892825e+00
Final optimality gap (abs / rel) = 0.00e+00 / 0.00e+00 (0.00%)
# of nodes processed = 5
# of subproblems processed = 11 (0.006s)
# of strong branching evaluations = 2 (0.010s)
Total program time (secs) = 0.01377 (0.041 CPU time)
Time spent in evaluations (secs) = 0.00004
Cuts statistics (computed / added)
----------------------------------
Knapsack cuts = 0 / 0
Mixed-Integer Rounding cuts = 0 / 0
Heuristics statistics (calls / sucesses / time)
-----------------------------------------------
Feasibility pump = 1 / 1 / 0.002
Rounding heuristic = 1 / 1 / 0.002
MPEC heuristic = 1 / 1 / 0.004
Display of Solution Vector and Constraints
If outlev equals 5 or 6, the values of the solution vector are printed
after the final statistics. If outlev equals 6, the constraint values
at the solution are also printed.
Solution Vector
---------------
x[0] = 1.30097589089e+00
x[1] = 0.00000000000e+00
x[2] = 1.00000000000e+00
x[3] = 0.00000000000e+00 (binary variable)
x[4] = 1.00000000000e+00 (binary variable)
x[5] = 0.00000000000e+00 (binary variable)
Getting information programmatically in callable library
Important solution information from Knitro can be retrieved through special API function calls.
Information related to the final statistics can be retrieved through the following function calls. The precise meaning of each function is described in the reference manual (Callable library API reference).
int KNITRO_API KN_get_number_FC_evals (const KN_context_ptr kc,
int * const numFCevals);
int KNITRO_API KN_get_number_GA_evals (const KN_context_ptr kc,
int * const numGAevals);
int KNITRO_API KN_get_number_H_evals (const KN_context_ptr kc,
int * const numHevals);
int KNITRO_API KN_get_number_HV_evals (const KN_context_ptr kc,
int * const numHVevals);
int KNITRO_API KN_get_solution (const KN_context_ptr kc,
int * const status,
double * const obj,
double * const x,
double * const lambda);
int KNITRO_API KN_get_obj_value (const KN_context_ptr kc,
double * const obj);
int KNITRO_API KN_get_con_values (const KN_context_ptr kc,
const KNINT nC,
const KNINT * const indexCons,
double * const c);
int KNITRO_API KN_get_rsd_values (const KN_context_ptr kc,
const KNINT nR,
const KNINT * const indexRsds,
double * const r);
Continuous problems
int KNITRO_API KN_get_number_iters (const KN_context_ptr kc,
int * const numIters);
int KNITRO_API KN_get_number_cg_iters (const KN_context_ptr kc,
int * const numCGiters);
int KNITRO_API KN_get_abs_feas_error (const KN_context_ptr kc,
double * const absFeasError);
int KNITRO_API KN_get_rel_feas_error (const KN_context_ptr kc,
double * const relFeasError);
int KNITRO_API KN_get_abs_opt_error (const KN_context_ptr kc,
double * const absOptError);
int KNITRO_API KN_get_rel_opt_error (const KN_context_ptr kc,
double * const relOptError);
int KNITRO_API KN_get_objgrad_nnz (const KN_context_ptr kc,
KNINT * const nnz);
int KNITRO_API KN_get_objgrad_values (const KN_context_ptr kc,
KNINT * const indexVars,
double * const objGrad);
int KNITRO_API KN_get_objgrad_values_all (const KN_context_ptr kc,
double * const objGrad);
int KNITRO_API KN_get_jacobian_nnz (const KN_context_ptr kc,
KNLONG * const nnz);
int KNITRO_API KN_get_jacobian_values (const KN_context_ptr kc,
KNINT * const indexCons,
KNINT * const indexVars,
double * const jac);
int KNITRO_API KN_get_rsd_jacobian_nnz (const KN_context_ptr kc,
KNLONG * const nnz);
int KNITRO_API KN_get_rsd_jacobian_values (const KN_context_ptr kc,
KNINT * const indexRsds,
KNINT * const indexVars,
double * const rsdJac);
int KNITRO_API KN_get_hessian_nnz (const KN_context_ptr kc,
KNLONG * const nnz);
int KNITRO_API KN_get_hessian_values (const KN_context_ptr kc,
KNINT * const indexVars1,
KNINT * const indexVars2,
double * const hess);
Discrete or mixed integer problems
int KNITRO_API KN_get_mip_number_nodes (const KN_context_ptr kc,
int * const numNodes);
int KNITRO_API KN_get_mip_number_solves (const KN_context_ptr kc,
int * const numSolves);
int KNITRO_API KN_get_mip_abs_gap (const KN_context_ptr kc,
double * const absGap);
int KNITRO_API KN_get_mip_rel_gap (const KN_context_ptr kc,
double * const relGap);
int KNITRO_API KN_get_mip_incumbent_obj (const KN_context_ptr kc,
double * const incumbentObj);
int KNITRO_API KN_get_mip_relaxation_bnd (const KN_context_ptr kc,
double * const relaxBound);
int KNITRO_API KN_get_mip_lastnode_obj (const KN_context_ptr kc,
double * const lastNodeObj);
int KNITRO_API KN_get_mip_incumbent_x (const KN_context_ptr kc,
double * const x);
Getting information programmatically in the object-oriented interface
Solution information can be retrieved after a call to
KNSolver::solve(). After solve() is called, KNSolver::getObj()
returns the objective function value, and KNSolver::getSolution() return the final primal and
and dual variable values. The solution status code
is returned by KNSolver::getSolution() method.
In addition, information related to the final statistics can be
retrieved through the following KNSolver methods.
The precise meaning of each function is described in the reference manual
(Callable library API reference).
int KNSolver::getNumberFCEvals();
int KNSolver::getNumberGAEvals();
int KNSolver::getNumberHEvals();
int KNSolver::getNumberHVEvals();
std::vector<double> KNSolver::getConstraintValues();
Continuous problems
int KNSolver::getNumberIters();
int KNSolver::getNumberCGIters();
double KNSolver::getAbsFeasError();
double KNSolver::getRelFeasError();
double KNSolver::getAbsOptError();
double KNSolver::getRelOptError();
std::vector<double> KNSolver::getObjgradValues();
KNQuadraticStructure KNSolver::getJacobianValues();
KNQuadraticStructure KNSolver::getHessianValues();
Discrete or mixed integer problems
int KNSolver::getMipNumNodes();
int KNSolver::getMipNumSolves();
double KNSolver::getMipAbsGap();
double KNSolver::getMipRelGap();
double KNSolver::getMipIncumbentObj();
std::vector<double> KNSolver::getMipIncumbentX );
double KNSolver::getMipRelaxationBnd();
double KNSolver::getMipLastnodeObj();
User-defined names in Knitro output
By default Knitro uses x for variable names and c for constraint names
in the output. However, the user can define more meaningful and customized names
for the objective function, the variables and the constraint functions through the
the API functions KN_set_obj_name(), KN_set_var_names(),
KN_set_con_names(), and KN_set_compcon_names()
when using the callable library API.
When using the AMPL modeling language, you can have Knitro output objective function, variable and constraint names specified in the AMPL model by issuing the following command in the AMPL session:
option knitroampl_auxfiles rc;
Suppressing all output in AMPL
Even when setting the options:
ampl: option solver_msg 0;
ampl: option knitro_options "outlev=0";
in an AMPL session, AMPL will still print some basic information like the solver name and non-default user option settings to the screen. In order to suppress all AMPL and Knitro output you must change your AMPL solve commands to something like:
ampl: solve >scratch-file;
where scratch-file is the name of some temporary file where the unwanted output can be sent. Under Unix, “solve >/dev/null” automatically throws away the unwanted output and under Windows, “solve > NUL” does the same.
AMPL solution information through suffixes
Some Knitro solution information can be retrieved and displayed through AMPL using AMPL suffixes defined for Knitro (see AMPL suffixes defined for Knitro). In particular, when solving a MIP using Knitro/AMPL, the best relaxation bound and the incumbent solution can be displayed using the relaxbnd and incumbent suffixes. For example, if the objective function is named obj, then:
ampl: display obj.relaxbnd;
give the current relaxation bound and:
ampl: display obj.incumbent;
will give the current incumbent solution (if one exists).
AMPL presolve
AMPL will often perform a reordering of the variables and constraints defined in the AMPL model. The AMPL presolver may also simplify the form of the problem by eliminating certain variables or constraints. The output printed by Knitro corresponds to the reordered, reformulated problem. To view final variable and constraint values in the original AMPL model, use the AMPL display command after Knitro has completed solving the problem.
It is possible to correlate Knitro variables and constraints with the original AMPL model. You must type an extra command in the AMPL session:
option knitroampl_auxfiles rc;
and set Knitro option presolve_dbg = 2. Then the solver will
print the variables and constraints that Knitro receives, with their
upper and lower bounds, and their AMPL model names. The extra AMPL command
causes the model names to be passed to the Knitro/AMPL solver.
The output below is obtained with the
example file testproblem.mod supplied with the distribution.
The center column of variable and constraint names are those used by
Knitro, while the names in the right-hand column are from the AMPL model:
ampl: model testproblem.mod;
ampl: option solver knitroampl;
ampl: option knitroampl_auxfiles rc;
ampl: option knitro_options "presolve_dbg=2 outlev=0";
Artelys Knitro 14.1.0: presolve_dbg=2
outlev=0
----- Problem seen by Knitro -----
Objective name: obj
0.000000e+00 <= x[ 0] <= 1.797693e+308 x[1]
0.000000e+00 <= x[ 1] <= 1.797693e+308 x[2]
0.000000e+00 <= x[ 2] <= 1.797693e+308 x[3]
2.500000e+01 <= c[ 0] <= 1.797693e+308 c2 (quadratic)
5.600000e+01 <= c[ 1] <= 5.600000e+01 c1 (linear)
-----------------------------------
Knitro 14.1.0: Locally optimal or satisfactory solution.
objective 936; feasibility error 0
10 iterations; 0 function evaluations