XPRSgetiisdata

Purpose

Returns information for an Irreducible Infeasible Set: size, variables (row and column vectors) and conflicting sides of the variables, duals and reduced costs.

Synopsis

int XPRS_CC XPRSgetiisdata(XPRSprob prob, int iis, int *p_nrows, int *p_ncols, int rowind[], int colind[], char contype[], char bndtype[], double duals[], double djs[], char isolationrows[], char isolationcols[]);

Arguments

prob

The current problem.

iis

The ordinal number of the IIS to get data for.

p_nrows

Pointer to an integer where the number of rows in the IIS will be returned.

p_ncols

Pointer to an integer where the number of bounds in the IIS will be returned.

rowind

Indices of rows in the IIS. Can be NULL if not required.

colind

Indices of bounds (columns) in the IIS. Can be NULL if not required.

contype

Sense of rows in the IIS:

L	for less or equal row;
G	for greater or equal row.
E	for an equality row (for a non LP IIS);
1	for a SOS1 row;
2	for a SOS2 row;
W	for a piecewise linear constraint;
X	for a general constraint;
I	for an indicator row.

Can be NULL if not required.

bndtype

Sense of bound in the IIS:

U	for upper bound;
L	for lower bound.
F	for fixed columns (for a non LP IIS);
B	for a binary column;
I	for an integer column;
P	for a partial integer columns;
S	for a semi-continuous column;
R	for a semi-continuous integer column.

Can be NULL if not required.

duals

The dual multipliers associated with the rows. Can be NULL if not required.

djs

The dual multipliers (reduced costs) associated with the bounds. Can be NULL if not required.

isolationrows

The isolation status of the rows:

-1	if isolation information is not available for row (run iis isolations);
0	if row is not in isolation;
1	if row is in isolation.

Can be NULL if not required.

isolationcols

The isolation status of the bounds:

-1	if isolation information is not available for column (run iis isolations);
0	if column is not in isolation;
1	if column is in isolation.

Can be NULL if not required.

Example

This example first retrieves the size of IIS 1, then gets the detailed information for the IIS.

XPRSgetiisdata(myprob, 1, &nrow, &ncol, NULL, NULL, NULL, NULL,
NULL,NULL,NULL,NULL);

rows = malloc(nrow*sizeof(int));
cols = malloc(ncol*sizeof(int));
contype = malloc(nrow);
bndtype = malloc(ncol);
duals = malloc(nrow*sizeof(double));
djs = malloc(ncol*sizeof(double));
isolationrows = malloc(nrow);
isolationcols = malloc(ncol);
XPRSgetiisdata(myprob, 1, &nrow, &ncol, rows, cols, contype,
               bndtype, duals, djs, isolationrows, isolationcols);

Further information

1. Calling IIS from the console automatically prints most of the above IIS information to the screen. Extra information can be printed with the IIS -p command.

2. IISs are numbered from 1 to NUMIIS. Index number 0 refers to the IIS approximation.

3. If rowind and colind both are NULL, only the p_nrows and p_ncols are returned.

4. The arrays may be NULL if not required. However, arrays contype, duals and isolationrows are only returned if rowind is not NULL. Similarly, arrays bndtype, djs and isolationcols are only returned if colind is not NULL.

5. All the non NULL arrays should be of length p_nrows or p_ncols, respectively.

6. For the initial IIS approximation ( iis = 0) the number of rows and columns with a nonzero Lagrange multiplier (dual/reduced cost respectively) are returned. Please note that, in such cases, it might be necessary to call XPRSiisstatus to retrieve the necessary size of the return arrays.

7. If there are Special Ordered Sets in the IIS, their number is included in the rowind array.

8. For non LP IISs, some column indices may appear more than once in the colind array, for example an integrality and a bound restriction for the same column.

9. Duals, reduced cost and isolation information is not available for nonlinear IIS problems, and for those the arrays are filled with zero values in case they are provided.

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