/*------------------------------------------------------------------------*/
/* File: examples/src/lpex6.c */
/* Version 8.1 */
/*------------------------------------------------------------------------*/
/* Copyright (C) 1997-2002 by ILOG. */
/* All Rights Reserved. */
/* Permission is expressly granted to use this example in the */
/* course of developing applications that use ILOG products. */
/*------------------------------------------------------------------------*/
/* lpex6.c - Illustrates that optimal basis can be copied and
used to start an optimization. */
/* Bring in the CPLEX function declarations and the C library
header file stdio.h with the following single include. */
#include <ilcplex/cplex.h>
/* Bring in the declarations for the string functions */
#include <string.h>
/* Include declaration for function at end of program */
static int
populatebycolumn (CPXENVptr env, CPXLPptr lp);
/* The problem we are optimizing will have 2 rows, 3 columns
and 6 nonzeros. */
#define NUMROWS 2
#define NUMCOLS 3
#define NUMNZ 6
int
main (void)
{
char probname[16]; /* Problem name is max 16 characters */
int cstat[NUMCOLS];
int rstat[NUMROWS];
/* Declare and allocate space for the variables and arrays where we
will store the optimization results including the status, objective
value, variable values, dual values, row slacks and variable
reduced costs. */
int solstat;
double objval;
double x[NUMCOLS];
double pi[NUMROWS];
double slack[NUMROWS];
double dj[NUMCOLS];
CPXENVptr env = NULL;
CPXLPptr lp = NULL;
int status;
int i, j;
int cur_numrows, cur_numcols;
/* Initialize the CPLEX environment */
env = CPXopenCPLEX (&status);
/* If an error occurs, the status value indicates the reason for
failure. A call to CPXgeterrorstring will produce the text of
the error message. Note that CPXopenCPLEX produces no output,
so the only way to see the cause of the error is to use
CPXgeterrorstring. For other CPLEX routines, the errors will
be seen if the CPX_PARAM_SCRIND indicator is set to CPX_ON. */
if ( env == NULL ) {
char errmsg[1024];
fprintf (stderr, "Could not open CPLEX environment.\n");
CPXgeterrorstring (env, status, errmsg);
fprintf (stderr, "%s", errmsg);
goto TERMINATE;
}
/* Turn on output to the screen */
status = CPXsetintparam (env, CPX_PARAM_SCRIND, CPX_ON);
if ( status ) {
fprintf (stderr,
"Failure to turn on screen indicator, error %d.\n", status);
goto TERMINATE;
}
/* Create the problem. */
strcpy (probname, "example");
lp = CPXcreateprob (env, &status, probname);
/* A returned pointer of NULL may mean that not enough memory
was available or there was some other problem. In the case of
failure, an error message will have been written to the error
channel from inside CPLEX. In this example, the setting of
the parameter CPX_PARAM_SCRIND causes the error message to
appear on stdout. */
if ( lp == NULL ) {
fprintf (stderr, "Failed to create LP.\n");
goto TERMINATE;
}
/* Now populate the problem with the data. */
status = populatebycolumn (env, lp);
if ( status ) {
fprintf (stderr, "Failed to populate problem data.\n");
goto TERMINATE;
}
/* We assume we know the optimal basis. Variables 1 and 2 are basic,
while variable 0 is at its upper bound */
cstat[0] = CPX_AT_UPPER;
cstat[1] = CPX_BASIC;
cstat[2] = CPX_BASIC;
/* The row statuses are all nonbasic for this problem */
rstat[0] = CPX_AT_LOWER;
rstat[1] = CPX_AT_LOWER;
/* Now copy the basis */
status = CPXcopybase (env, lp, cstat, rstat);
if ( status ) {
fprintf (stderr, "Failed to copy the basis.\n");
goto TERMINATE;
}
/* Optimize the problem and obtain solution. */
status = CPXlpopt (env, lp);
if ( status ) {
fprintf (stderr, "Failed to optimize LP.\n");
goto TERMINATE;
}
status = CPXsolution (env, lp, &solstat, &objval, x, pi, slack, dj);
if ( status ) {
fprintf (stderr, "Failed to obtain solution.\n");
goto TERMINATE;
}
/* Write the output to the screen. */
printf ("\nSolution status = %d\n", solstat);
printf ("Solution value = %f\n", objval);
printf ("Iteration count = %d\n\n", CPXgetitcnt (env, lp));
/* The size of the problem should be obtained by asking CPLEX what
the actual size is, rather than using sizes from when the problem
was built. cur_numrows and cur_numcols store the current number
of rows and columns, respectively. */
cur_numrows = CPXgetnumrows (env, lp);
cur_numcols = CPXgetnumcols (env, lp);
for (i = 0; i < cur_numrows; i++) {
printf ("Row %d: Slack = %10f Pi = %10f\n", i, slack[i], pi[i]);
}
for (j = 0; j < cur_numcols; j++) {
printf ("Column %d: Value = %10f Reduced cost = %10f\n",
j, x[j], dj[j]);
}
/* Finally, write a copy of the problem to a file. */
status = CPXwriteprob (env, lp, "lpex6.sav", NULL);
if ( status ) {
fprintf (stderr, "Failed to write LP to disk.\n");
goto TERMINATE;
}
TERMINATE:
/* Free up the problem as allocated by CPXcreateprob, if necessary */
if ( lp != NULL ) {
status = CPXfreeprob (env, &lp);
if ( status ) {
fprintf (stderr, "CPXfreeprob failed, error code %d.\n", status);
}
}
/* Free up the CPLEX environment, if necessary */
if ( env != NULL ) {
status = CPXcloseCPLEX (&env);
/* Note that CPXcloseCPLEX produces no output,
so the only way to see the cause of the error is to use
CPXgeterrorstring. For other CPLEX routines, the errors will
be seen if the CPX_PARAM_SCRIND indicator is set to CPX_ON. */
if ( status ) {
char errmsg[1024];
fprintf (stderr, "Could not close CPLEX environment.\n");
CPXgeterrorstring (env, status, errmsg);
fprintf (stderr, "%s", errmsg);
}
}
return (status);
} /* END main */
/* This function builds by column the linear program:
Maximize
obj: x1 + 2 x2 + 3 x3
Subject To
c1: - x1 + x2 + x3 <= 20
c2: x1 - 3 x2 + x3 <= 30
Bounds
0 <= x1 <= 40
End
*/
static int
populatebycolumn (CPXENVptr env, CPXLPptr lp)
{
int status = 0;
double obj[NUMCOLS];
double lb[NUMCOLS];
double ub[NUMCOLS];
char *colname[NUMCOLS];
int matbeg[NUMCOLS];
int matind[NUMNZ];
double matval[NUMNZ];
double rhs[NUMROWS];
char sense[NUMROWS];
char *rowname[NUMROWS];
/* To build the problem by column, create the rows, and then
add the columns. */
CPXchgobjsen (env, lp, CPX_MAX); /* Problem is maximization */
/* Now create the new rows. First, populate the arrays. */
rowname[0] = "c1";
sense[0] = 'L';
rhs[0] = 20.0;
rowname[1] = "c2";
sense[1] = 'L';
rhs[1] = 30.0;
status = CPXnewrows (env, lp, NUMROWS, rhs, sense, NULL, rowname);
if ( status ) goto TERMINATE;
/* Now add the new columns. First, populate the arrays. */
obj[0] = 1.0; obj[1] = 2.0; obj[2] = 3.0;
matbeg[0] = 0; matbeg[1] = 2; matbeg[2] = 4;
matind[0] = 0; matind[2] = 0; matind[4] = 0;
matval[0] = -1.0; matval[2] = 1.0; matval[4] = 1.0;
matind[1] = 1; matind[3] = 1; matind[5] = 1;
matval[1] = 1.0; matval[3] = -3.0; matval[5] = 1.0;
lb[0] = 0.0; lb[1] = 0.0; lb[2] = 0.0;
ub[0] = 40.0; ub[1] = CPX_INFBOUND; ub[2] = CPX_INFBOUND;
colname[0] = "x1"; colname[1] = "x2"; colname[2] = "x3";
status = CPXaddcols (env, lp, NUMCOLS, NUMNZ, obj, matbeg, matind,
matval, lb, ub, colname);
if ( status ) goto TERMINATE;
TERMINATE:
return (status);
} /* END populatebycolumn */
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