/***********************************************************************
Xpress Optimizer Examples
=========================
file trimloss.c
```````````````
Modify a problem by adding an extra variable within an additional
constraint.
We take a trimloss problem in which each integer variable x(p)
represents the number of rolls cut to pattern p.
We define a new integer variable y=SUM(p)x(p) and add the associated
constraint
x(1)+x(2)+...+x(N)-y = 0
We do this by first adding a row containing the (unitary)
coefficients of the x(p), and then a column corresponding to y.
We output the revised matrix to a file and then solve the revised
MIP, giving y the highest branching priority. Finally, we output
the solution, both to the screen and to an ASCII solution file.
(c) 2017-2025 Fair Isaac Corporation
***********************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "xprs.h" /* Optimizer header file */
/* Calls an Xpress optimizer function and checks the return code.
* If the call fails then the function
* - prints a short error message to stderr,
* - sets variable 'returnCode' to the error,
* - and branches to label 'cleanup'.
*/
#define CHECK_RETURN(call) do { \
int result_ = call; \
if ( result_ != 0 ) { \
fprintf(stderr, "Line %d: %s failed with %d\n", \
__LINE__, #call, result_); \
returnCode = result_; \
goto cleanup; \
} \
} while (0)
static void XPRS_CC messagecb(XPRSprob cbprob, void* cbdata,
const char *msg, int len, int msgtype);
int main()
{
int returnCode = 0;
XPRSprob prob = NULL; /* The problem instance */
char sProblem[]="../data/trimloss"; /* Problem name */
char sLogFile[]="trimloss.log"; /* Log file name */
int nRow; /* Number of rows */
int nCol; /* Number of columns */
int i; /* Loop counter */
/* New row variables */
int nNewRow = 1; /* Number of new rows */
int nRowElem; /* Number of non-zero elements in the new row */
double *pRowVal; /* Values of the new row elements */
int *pColInd = NULL; /* Column indices of the new row elements */
int nRowStart[1]; /* Start position of the row in pRowVal */
char sRowType[1]; /* New row type */
double dRHS[1]; /* New RHS value */
char sRowName[9]; /* New row name */
/* New column variables */
int nNewCol = 1; /* Number of new columns */
int nColElem; /* Number of non-zero elements in the new column */
double *pColVal = NULL; /* Values of the new column elements */
int *pRowInd = NULL; /* Row indices of the new column elements */
int nColStart[1]; /* Start position of the column in pColVal */
double dObjCoef[1]; /* Objective coefficient of the new column */
double dUpperBnd[1]; /* Upper bound on the new column */
double dLowerBnd[1]; /* Lower bound on the new column */
char sColType[1]; /* New column type */
int nNewColInd[1]; /* New column index */
int nTypeChg = 1; /* Number of column types to change - to make y
an integer variable */
char sColName[9]; /* New column name */
int nColPrior[1]; /* Branching priority of the new column */
/* Solution variables */
double dObjVal; /* Objective value of the best integer solution found
*/
double *x = NULL; /* Primal solution values */
/* Initialize the optimizer. */
if ( XPRSinit("") != 0 ) {
char message[512];
XPRSgetlicerrmsg(message, sizeof(message));
fprintf(stderr, "Licensing error: %s\n", message);
return 1;
}
/* Create a new problem and immediately register a message handler.
* Once we have a message handler installed, errors will produce verbose
* error messages on the console and we can limit ourselves to minimal
* error handling in the code here.
*/
CHECK_RETURN( XPRScreateprob(&prob) );
CHECK_RETURN( XPRSaddcbmessage(prob, messagecb, NULL, 0) );
/* Remove and define log file */
remove(sLogFile);
CHECK_RETURN( XPRSsetlogfile(prob, sLogFile) );
/* Turn off presolve and permit no cuts */
CHECK_RETURN( XPRSsetintcontrol(prob, XPRS_PRESOLVE, 0) );
CHECK_RETURN( XPRSsetintcontrol(prob, XPRS_CUTSTRATEGY, 0) );
/* Read the problem file */
CHECK_RETURN( XPRSreadprob(prob, sProblem,"") );
/* Get the number of rows and columns */
CHECK_RETURN( XPRSgetintattrib(prob, XPRS_ROWS, &nRow) );
CHECK_RETURN( XPRSgetintattrib(prob, XPRS_COLS, &nCol) );
/*** Construct and add the new row ***/
/* Assign the number of new row elements*/
nRowElem = nCol;
/* Allocate memory for the new row arrays */
pRowVal=malloc(nRowElem * sizeof(*pRowVal));
pColInd=malloc(nRowElem * sizeof(*pColInd));
if (!pRowVal || !pColInd) {
perror("malloc");
returnCode = -2;
goto cleanup;
}
/* Construct the new row */
dRHS[0] = 0.0;
nRowStart[0] = 0;
sRowType[0] = 'E';
/* Store the coefficents of the x(p) */
for (i = 0; i < nCol; i++) {
pRowVal[i] = 1.0;
pColInd[i] = i;
}
/* Add the new row */
CHECK_RETURN( XPRSaddrows(prob, nNewRow, nRowElem, sRowType, dRHS, NULL,
nRowStart, pColInd, pRowVal) );
/* Update the number of rows */
CHECK_RETURN( XPRSgetintattrib(prob, XPRS_ROWS, &nRow) );
/* Add new row name */
strcpy(sRowName,"NewRow");
CHECK_RETURN( XPRSaddnames(prob, 1, sRowName, nRow-1, nRow-1) );
/*** Construct and add the new column ***/
/* Assign the number of new column elements*/
nColElem = 1;
/* Allocate memory for the new column arrays */
pColVal=malloc(nColElem * sizeof(*pColVal));
pRowInd=malloc(nColElem * sizeof(*pRowInd));
if (!pColVal || !pRowInd ) {
perror("malloc");
returnCode = -2;
goto cleanup;
}
/* Construct the new column */
dObjCoef[0] = 0.0;
nColStart[0] = 0;
pColVal[0] = -1.0; /* the coefficent of -y */
pRowInd[0] = nRow-1;
dLowerBnd[0] = 0.0;
dUpperBnd[0] = 90; /* the sum of the bounds on the x(p) */
/* Add the new column */
CHECK_RETURN( XPRSaddcols(prob, nNewCol, nColElem, dObjCoef, nColStart,
pRowInd, pColVal, dLowerBnd, dUpperBnd) );
/* Update the number of columns */
CHECK_RETURN( XPRSgetintattrib(prob, XPRS_COLS, &nCol) );
/* Make the new column an integer variable */
nTypeChg=1;
nNewColInd[0]=nCol-1;
sColType[0]= 'I';
CHECK_RETURN( XPRSchgcoltype(prob, nTypeChg, nNewColInd, sColType) );
/* Add new column name */
strcpy(sColName,"y");
CHECK_RETURN( XPRSaddnames(prob, 2, sColName, nCol-1, nCol-1) );
/*** Output the revised matrix ***/
CHECK_RETURN( XPRSwriteprob(prob,"revised","") );
/*** Solve the revised MIP ***/
/* Assign the y variable a high branching priority (1)
- by default the original x(p) variables have low priority (500) */
nColPrior[0] = 1;
/* Load this directive */
CHECK_RETURN( XPRSloaddirs(prob, 1, nNewColInd, nColPrior, NULL, NULL, NULL)
);
/* Solve the MIP */
printf("Solving problem %s:\n\n", sProblem);
CHECK_RETURN( XPRSmipoptimize(prob,"") );
/* Get the objective value of the best integer solution found */
CHECK_RETURN( XPRSgetdblattrib(prob, XPRS_MIPOBJVAL, &dObjVal) );
/* Allocate memory to the solution array */
x = malloc(nCol*sizeof(*x));
if (!x) {
perror("malloc");
returnCode = -2;
goto cleanup;
}
/* Get the primal solution values */
CHECK_RETURN( XPRSgetsolution(prob, NULL, x, 0, nCol - 1) );
/* Display the objective and solution values */
printf(" Minimum loss is %g\n\n", dObjVal);
printf(" The solution values are\n");
for(i = 0; i < nCol-1; i++)
printf(" x(%d)=%g\n", i+1, x[i]);
printf(" y = %g\n\n", x[nCol-1]);
/* Save the solution to an ASCII file */
CHECK_RETURN( XPRSwritesol(prob,"revised","") );
cleanup:
if (returnCode > 0) {
/* There was an error with the solver. Get the error code and error message.
* If prob is still NULL then the error was in XPRScreateprob() and
* we cannot find more detailed error information.
*/
if (prob != NULL) {
int errorCode = -1;
char errorMessage[512] = {0};
XPRSgetintattrib(prob, XPRS_ERRORCODE, &errorCode);
XPRSgetlasterror(prob, errorMessage);
fprintf(stderr, "Error %d: %s\n", errorCode, errorMessage);
}
}
/* Free the resources (variables are initialized so that this is valid
* even in case of error).
*/
free(pRowVal);
free(pColInd);
free(pColVal);
free(pRowInd);
free(x);
XPRSdestroyprob(prob);
XPRSfree();
return returnCode;
}
/* XPRS optimizer message callback */
void XPRS_CC messagecb(XPRSprob cbprob, void* cbdata,
const char *msg, int len, int msgtype)
{
(void)cbprob; /* unused (the problem for which the message is issued) */
(void)cbdata; /* unused (the data passed to XPRSaddcbmessage()) */
switch(msgtype)
{
case 4: /* error */
case 3: /* warning */
case 2: /* not used */
case 1: /* information */
printf("%*s\n", len, msg);
break;
default: /* exiting - buffers need flushing */
fflush(stdout);
break;
}
}
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