static int
buildnetwork (CPXENVptr env, CPXLPptr lp)
{
char sense[NUMNODES];
double rhs[NUMNODES];
int ind[2];
double val[2];
char *name[1];
char buffer[100];
int i, j, varindex;
int zero = 0;
double dblzero = 0.0;
double dblone = 1.0;
char binary = 'B';
int status = 0;
/* Create constraint placeholders ---
One constraint for each node (flow constraints)
*/
for (i = 0; i < NUMNODES; i++) {
rhs[i] = demand[i];
sense[i] = 'G';
}
status = CPXnewrows (env, lp, NUMNODES, rhs, sense, NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not create new rows.\n");
goto TERMINATE;
}
/* Add flow variables */
for (j = 0; j < NUMEDGES; j++) {
ind[0] = orig[j]; /* Flow leaves origin */
val[0] = -1.0;
ind[1] = dest[j]; /* Flow arrives at destination */
val[1] = 1.0;
name[0] = buffer;
sprintf(buffer, "x%d%d", orig[j], dest[j]);
status = CPXaddcols (env, lp, 1, 2, &unitcost[j], &zero, ind, val,
NULL, NULL, name);
if ( status ) {
fprintf (stderr, "Failed to add flow edge.\n");
goto TERMINATE;
}
}
/* Add fixed charge variables */
for (j = 0; j < NUMEDGES; j++) {
name[0] = buffer;
sprintf(buffer, "f%d%d", orig[j], dest[j]);
status = CPXaddcols (env, lp, 1, 0, &fixedcost[j], &zero, ind, val,
&dblzero, &dblone, name);
if ( status ) {
fprintf (stderr, "Failed to add fixed charge variable.\n");
goto TERMINATE;
}
varindex = NUMEDGES+j;
status = CPXchgctype (env, lp, 1, &varindex, &binary);
if ( status ) {
fprintf (stderr, "Failed to change variable type.\n");
goto TERMINATE;
}
}
/* Add indicator constraints --
f = 0 -> x <= 0 */
for (j = 0; j < NUMEDGES; j++) {
varindex = j;
sprintf(buffer, "indicator%d", j);
status = CPXaddindconstr (env, lp, NUMEDGES+j, 1, 1,
0.0, 'L', &varindex, &dblone, buffer);
if ( status ) {
fprintf (stderr, "Failed to add indicator constraint.");
goto TERMINATE;
}
}
TERMINATE:
return (status);
} /* END buildnetwork */
static int
buildmodel (CPXENVptr env, CPXLPptr lp)
{
int colcnt = NUMVARS*NUMMONTHS*NUMPRODUCTS;
double *obj = NULL;
double *lb = NULL;
double *ub = NULL;
char *ctype = NULL;
int *rmatind = NULL;
double *rmatval = NULL;
int indicator;
int rmatbeg[1];
double rhs[1];
char sense[1];
int m, p;
int status = 0;
status = CPXchgobjsen (env, lp, CPX_MAX); /* Maximization problem */
if ( status ) {
fprintf (stderr, "Could not change objective sense.\n");
goto TERMINATE;
}
rmatbeg[0] = 0;
/* Allocate colcnt-sized arrays */
obj = (double *) malloc (colcnt * sizeof(double));
lb = (double *) malloc (colcnt * sizeof(double));
ub = (double *) malloc (colcnt * sizeof(double));
ctype = (char *) malloc (colcnt * sizeof(char));
rmatind = (int * ) malloc (colcnt * sizeof(int));
rmatval = (double *) malloc (colcnt * sizeof(double));
if ( obj == NULL ||
lb == NULL ||
ub == NULL ||
ctype == NULL ||
rmatind == NULL ||
rmatval == NULL ) {
fprintf (stderr, "Could not allocate colcnt arrays\n");
status = CPXERR_NO_MEMORY;
goto TERMINATE;
}
/* Create variables. For each month and each product, we have 3
variables corresponding to the quantity used (semi-continuous),
stored (continuous) and bought (continuous) and one binary
variable indicating whether or not the product is used during
this month. */
for (m = 0; m < NUMMONTHS; m++) {
for (p = 0; p < NUMPRODUCTS; p++) {
/* The quantity bought is a continuous variable. It has a cost */
obj[varindex(m, p, BUY)] = -cost[m*NUMPRODUCTS + p];
lb[varindex (m, p, BUY)] = 0.0;
ub[varindex (m, p, BUY)] = CPX_INFBOUND;
ctype[varindex (m, p, BUY)] = 'C';
/* When an oil is used, the quantity must be at least 20
tons. This is modeled as a semi-continuous variable. */
obj[varindex (m, p, USE)] = 0.0;
lb[varindex (m, p, USE)] = 20.0;
ub[varindex (m, p, USE)] = CPX_INFBOUND;
ctype[varindex (m, p, USE)] = 'S';
/* It is possible to store up to 1000 tons of each
product. There are storage costs. */
obj[varindex (m, p, STORE)] = -5.0;
lb[varindex (m, p, STORE)] = 0.0;
ub[varindex (m, p, STORE)] = 1000.0;
ctype[varindex (m, p, STORE)] = 'C';
/* At the end, we must have exactly 500 tons of each
product in storage. */
if ( m == NUMMONTHS - 1 ) {
lb[varindex (m, p, STORE)] = 500.0;
ub[varindex (m, p, STORE)] = 500.0;
}
/* The variable indicating whether or not a product is
used during a month is a binary variable. */
obj[varindex (m, p, IS_USED)] = 0.0;
lb[varindex (m, p, IS_USED)] = 0.0;
ub[varindex (m, p, IS_USED)] = 1.0;
ctype[varindex (m, p, IS_USED)] = 'B';
}
}
status = CPXnewcols (env, lp, colcnt, obj, lb, ub, ctype, NULL);
if ( status ) {
fprintf (stderr, "Could not add new columns.\n");
goto TERMINATE;
}
/* Constraints for each month */
for (m = 0; m < NUMMONTHS; m++) {
int totalindex;
/* For each product, create an indicator constraint linking the
quantity used and the binary variable indicating whether or
not the product is used */
for (p = 0; p < NUMPRODUCTS; p++) {
indicator = varindex (m, p, IS_USED);
rmatind[0] = varindex (m, p, USE);
rmatval[0] = 1.0;
status = CPXaddindconstr (env, lp, indicator, 1, 1, 0.0, 'L',
rmatind, rmatval, NULL);
if ( status ) {
fprintf (stderr, "Could not add new indicator constraint.\n");
goto TERMINATE;
}
}
/* Not more than 200 tons of vegetable oil can be refined */
rmatind[0] = varindex (m, VEGOIL1, USE);
rmatind[1] = varindex (m, VEGOIL2, USE);
rmatval[0] = 1.0;
rmatval[1] = 1.0;
rhs[0] = 200.0;
sense[0] = 'L';
status = CPXaddrows (env, lp, 0, 1, 2, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
/* Not more than 250 tons of non-vegetable oil can be refined */
rmatind[0] = varindex (m, OIL1, USE);
rmatind[1] = varindex (m, OIL2, USE);
rmatind[2] = varindex (m, OIL3, USE);
rmatval[0] = 1.0;
rmatval[1] = 1.0;
rmatval[2] = 1.0;
rhs[0] = 250.0;
sense[0] = 'L';
status = CPXaddrows (env, lp, 0, 1, 3, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
/* Constraint on food composition */
/* Add a variable corresponding to total quantity produced
in a month */
obj[0] = 150.0;
lb[0] = 0.0;
ub[0] = CPX_INFBOUND;
ctype[0] = 'C';
status = CPXnewcols (env, lp, 1, obj, lb, ub, ctype, NULL);
if ( status ) {
fprintf (stderr, "Could not add new columns.\n");
goto TERMINATE;
}
totalindex = CPXgetnumcols (env, lp) - 1;
/* Total quantity = sum (quantities) */
for (p = 0; p < NUMPRODUCTS; p++) {
rmatind[p] = varindex (m, p, USE);
rmatval[p] = 1.0;
}
rmatind[NUMPRODUCTS] = totalindex;
rmatval[NUMPRODUCTS] = -1.0;
rhs[0] = 0.0;
sense[0] = 'E';
status = CPXaddrows (env, lp, 0, 1, NUMPRODUCTS + 1, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
/* Hardness constraints
sum (quantity * hardness) >= 3 * total quantity
sum (quantity * hardness) <= 6 * total quantity
*/
for (p = 0; p < NUMPRODUCTS; p++) {
rmatind[p] = varindex (m, p, USE);
rmatval[p] = hardness[p];
}
rmatind[NUMPRODUCTS] = totalindex;
rmatval[NUMPRODUCTS] = -3.0;
rhs[0] = 0.0;
sense[0] = 'G';
status = CPXaddrows (env, lp, 0, 1, NUMPRODUCTS + 1, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
rmatval[NUMPRODUCTS] = -6.0;
sense[0] = 'L';
status = CPXaddrows (env, lp, 0, 1, NUMPRODUCTS + 1, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
/* The food may never be made up of more than three oils */
for (p = 0; p < NUMPRODUCTS; p++) {
rmatind[p] = varindex (m, p, IS_USED);
rmatval[p] = 1.0;
}
rhs[0] = 3.0;
sense[0] = 'L';
status = CPXaddrows (env, lp, 0, 1, NUMPRODUCTS, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
/* If product veg 1 or veg 2 is used then oil 3 must be used */
indicator = varindex (m, VEGOIL1, IS_USED);
rmatind[0] = varindex (m, OIL3, USE);
rmatval[0] = 1.0;
status = CPXaddindconstr (env, lp, indicator, 0, 1, 20.0, 'G',
rmatind, rmatval, NULL);
indicator = varindex (m, VEGOIL2, IS_USED);
status = CPXaddindconstr (env, lp, indicator, 0, 1, 20.0, 'G',
rmatind, rmatval, NULL);
if ( status ) {
fprintf (stderr, "Could not add new indicator constraint.\n");
goto TERMINATE;
}
/* We can store each product from one month to the next,
starting with a stock of 500 tons */
for (p = 0; p < NUMPRODUCTS; p++) {
int n = 0;
if ( m != 0 ) {
rmatind[n] = varindex (m-1, p, STORE); /* stored last month */
rmatval[n++] = 1.0;
rmatind[n] = varindex (m, p, BUY); /* bought this month */
rmatval[n++] = 1.0;
rmatind[n] = varindex (m, p, USE); /* used this month */
rmatval[n++] = -1.0;
rmatind[n] = varindex (m, p, STORE); /* stored this month */
rmatval[n++] = -1.0;
rhs[0] = 0.0;
sense[0] = 'E';
}
else {
rmatind[n] = varindex (m, p, BUY); /* bought this month */
rmatval[n++] = 1.0;
rmatind[n] = varindex (m, p, USE); /* used this month */
rmatval[n++] = -1.0;
rmatind[n] = varindex (m, p, STORE); /* stored this month */
rmatval[n++] = -1.0;
rhs[0] = -500.0;
sense[0] = 'E';
}
status = CPXaddrows (env, lp, 0, 1, n, rhs,
sense, rmatbeg, rmatind, rmatval,
NULL, NULL);
if ( status ) {
fprintf (stderr, "Could not add new rows.\n");
goto TERMINATE;
}
}
}
TERMINATE:
free_and_null ((char **)&obj);
free_and_null ((char **)&lb);
free_and_null ((char **)&ub);
free_and_null ((char **)&ctype);
free_and_null ((char **)&rmatind);
free_and_null ((char **)&rmatval);
return (status);
} /* END buildmodel */
