Problem Attributes

Topics covered in this chapter:

During the optimization process, various properties of the problem being solved are stored and made available to users of the Xpress NonLinear Libraries in the form of problem attributes. These can be accessed in much the same manner as the controls. Examples of problem attributes include the sizes of arrays, for which library users may need to allocate space before the arrays themselves are retrieved. A full list of the attributes available and their types may be found in this chapter.

Library users are provided with the following functions for obtaining the values of attributes:


XSLPgetintattrib	XSLPgetdblattrib
XSLPgetptrattrib	XSLPgetstrattrib

The attributes listed in this chapter are all prefixed with XSLP_. Most of them also exist within the Optimizer library with an NLP or SLP prefix, e.g., XPRS_NLPSOLSTATUS. It is possible to use the above functions with other attributes for the Xpress Optimizer (attributes prefixed with XPRS_). For details of the Optimizer attributes, see the Optimizer manual.

Example of the usage of the functions:

XSLPgetintattrib(Prob, XSLP_ITER, &nIter);
printf("The number of SLP iterations is %d\n", nIter);
XSLPgetdblattrib(Prob, XSLP_ERRORCOSTS, &Errors);
printf("and the total error cost is %lg\n", Errors);

The following is a list of all the Xpress NonLinear attributes:

XSLP_COEFFICIENTS, SLPCOEFFICIENTS	Number of nonlinear coefficients
XSLP_CURRENTDELTACOST, SLPCURRENTDELTACOST	Current value of penalty cost multiplier for penalty delta vectors
XSLP_CURRENTERRORCOST, SLPCURRENTERRORCOST	Current value of penalty cost multiplier for penalty error vectors
XSLP_DELTAS, SLPDELTAS	Number of delta vectors created during augmentation
XSLP_ECFCOUNT, SLPECFCOUNT	Number of infeasible constraints found at the point of linearization
XSLP_EQUALSCOLUMN, NLPEQUALSCOLUMN	Index of the reserved "=" column
XSLP_ERRORCOSTS, SLPERRORCOSTS	Total penalty costs in the solution
XSLP_EXPLOREDELTAS, SLPEXPLOREDELTAS	Number of variables with an exploration-type delta set up in the problem
XSLP_IFS, NLPIFS	Number of internal functions
XSLP_IMPLICITVARIABLES, NLPIMPLICITVARIABLES	Number of SLP variables appearing only in coefficients
XSLP_INTEGERDELTAS, SLPINTEGERDELTAS	Number of variables set up with an integer delta in the problem
XSLP_ITER, SLPITER	SLP iteration count
XSLP_JOBID, NLPJOBID	Unique identifier for the current job
XSLP_KEEPBESTITER, NLPKEEPBESTITER	The iteration in which the returned solution has been found.
XSLP_MINUSPENALTYERRORS, SLPMINUSPENALTYERRORS	Number of negative penalty error vectors
XSLP_MIPITER, SLPMIPITER	Total number of SLP iterations in MISLP
XSLP_MIPNODES, SLPMIPNODES	Number of nodes explored in MISLP. This includes any nodes for which a non-linear solve has been carried out.
XSLP_MIPPROBLEM	The underlying Optimizer MIP problem. XSLP_MIPPROBLEM is a reference of type XPRSprob, and should be used in MISLP callbacks to access MIP-specific Optimizer values (such as node and parent numbers).
XSLP_MIPSOLS, SLPMIPSOLS	Number of integer solutions found in MISLP. This includes solutions found during the tree search or any heuristics.
XSLP_MODELCOLS, NLPMODELCOLS	Number of model columns in the problem
XSLP_MODELROWS, NLPMODELROWS	Number of model rows in the problem
XSLP_MSSTATUS	Status of the mutlistart search
XSLP_NLPSTATUS, NLPSTATUS	The solution status of the problem.
XSLP_NONCONSTANTCOEFFS, SLPNONCONSTANTCOEFFS	Number of coefficients in the augmented problem that might change between SLP iterations
XSLP_NONLINEARCONSTRAINTS, NONLINEARCONSTRAINTS	Number of nonlinear constraints in the problem
XSLP_OBJVAL, NLPOBJVAL	Objective function value excluding any penalty costs
XSLP_OPTTIME, NLPOPTTIME	Time spent in optimization
XSLP_ORIGINALCOLS, NLPORIGINALCOLS	Number of model columns in the extended original problem
XSLP_ORIGINALROWS, NLPORIGINALROWS	Number of model rows in the extended original problem
XSLP_PENALTYDELTACOLUMN, SLPPENALTYDELTACOLUMN	Index of column costing the penalty delta row
XSLP_PENALTYDELTAROW, SLPPENALTYDELTAROW	Index of equality row holding the penalties for delta vectors
XSLP_PENALTYDELTAS, SLPPENALTYDELTAS	Number of penalty delta vectors
XSLP_PENALTYDELTATOTAL, SLPPENALTYDELTATOTAL	Total activity of penalty delta vectors
XSLP_PENALTYDELTAVALUE, SLPPENALTYDELTAVALUE	Total penalty cost attributed to penalty delta vectors
XSLP_PENALTYERRORCOLUMN, SLPPENALTYERRORCOLUMN	Index of column costing the penalty error row
XSLP_PENALTYERRORROW, SLPPENALTYERRORROW	Index of equality row holding the penalties for penalty error vectors
XSLP_PENALTYERRORS, SLPPENALTYERRORS	Number of penalty error vectors
XSLP_PENALTYERRORTOTAL, SLPPENALTYERRORTOTAL	Total activity of penalty error vectors
XSLP_PENALTYERRORVALUE, SLPPENALTYERRORVALUE	Total penalty cost attributed to penalty error vectors
XSLP_PLUSPENALTYERRORS, SLPPLUSPENALTYERRORS	Number of positive penalty error vectors
XSLP_PRESOLVEELIMINATIONS, NLPPRESOLVEELIMINATIONS	Number of SLP variables eliminated by XSLPpresolve
XSLP_PRESOLVESTATE	Indicates if the problem is presolved
XSLP_PRIMALINTEGRAL, NLPPRIMALINTEGRAL	Local primal integral of the solve
XSLP_SBXCONVERGED, SLPSBXCONVERGED	Number of step-bounded variables converged only on extended criteria
XSLP_SEMICONTDELTAS, SLPSEMICONTDELTAS	Number of variables with a minimum perturbation step set up in the problem
XSLP_SOLSTATUS, NLPSOLSTATUS	Indicates the type of solution returned by the solver.
XSLP_SOLVERSELECTED, LOCALSOLVERSELECTED	Includes information of which Xpress solver has been used to solve the problem
XSLP_STATUS, SLPSTATUS	Bitmap holding the problem convergence status
XSLP_STOPSTATUS, NLPSTOPSTATUS	Status of the optimization process.
XSLP_TOLSETS, SLPTOLSETS	Number of tolerance sets.
XSLP_TOTALEVALUATIONERRORS, NLPTOTALEVALUATIONERRORS	The total number of evaluation errors during the solve
XSLP_UCCONSTRAINEDCOUNT, SLPUCCONSTRAINEDCOUNT	Number of unconverged variables with coefficients in constraining rows
XSLP_UFINSTANCES	Number of user function instances
XSLP_UFS, NLPUFS	Number of user functions
XSLP_UNCONVERGED, SLPUNCONVERGED	Number of unconverged values
XSLP_USEDERIVATIVES, NLPUSEDERIVATIVES	Indicates whether numeric or analytic derivatives were used to create the linear approximations and solve the problem
XSLP_USERFUNCCALLS, NLPUSERFUNCCALLS	Number of calls made to user functions
XSLP_VALIDATIONINDEX_A, NLPVALIDATIONINDEX_A	Absolute validation index
XSLP_VALIDATIONINDEX_K, NLPVALIDATIONINDEX_K	Relative first order optimality validation index
XSLP_VALIDATIONINDEX_R, NLPVALIDATIONINDEX_R	Relative validation index
XSLP_VALIDATIONNETOBJ, NLPVALIDATIONNETOBJ	Net objective as calculated by validation
XSLP_VALIDATIONSTATUS, NLPVALIDATIONSTATUS	Feasiblity status of the current solution.
XSLP_VARIABLES, NLPVARIABLES	Number of SLP variables
XSLP_VERSIONDATE	Date of creation of Xpress NonLinear
XSLP_VSOLINDEX	Vertex solution index
XSLP_XPRSPROBLEM	The underlying Optimizer problem
XSLP_XSLPPROBLEM	The Xpress NonLinear problem
XSLP_ZEROESRESET, SLPZEROESRESET	Number of placeholder entries set to zero
XSLP_ZEROESRETAINED, SLPZEROESRETAINED	Number of potentially zero placeholders left untouched
XSLP_ZEROESTOTAL, SLPZEROESTOTAL	Number of potential zero placeholder entries

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Problem Attributes