void lpx_get_row_info(glp_prob *lp, int i, int *tagx, double *vx,
double *dx)
{ /* obtain row solution information */
if (tagx != NULL) *tagx = lpx_get_row_stat(lp, i);
if (vx != NULL) *vx = lpx_get_row_prim(lp, i);
if (dx != NULL) *dx = lpx_get_row_dual(lp, i);
return;
}
int lpx_prim_ratio_test(LPX *lp, int len, const int ind[],
const double val[], int how, double tol)
{ int i, k, m, n, p, t, typx, tagx;
double alfa_i, abs_alfa_i, big, eps, bbar_i, lb_i, ub_i, temp,
teta;
if (!lpx_is_b_avail(lp))
xfault("lpx_prim_ratio_test: LP basis is not available\n");
if (lpx_get_prim_stat(lp) != LPX_P_FEAS)
xfault("lpx_prim_ratio_test: current basic solution is not pri"
"mal feasible\n");
if (!(how == +1 || how == -1))
xfault("lpx_prim_ratio_test: how = %d; invalid parameter\n",
how);
m = lpx_get_num_rows(lp);
n = lpx_get_num_cols(lp);
/* compute the largest absolute value of the specified influence
coefficients */
big = 0.0;
for (t = 1; t <= len; t++)
{ temp = val[t];
if (temp < 0.0) temp = - temp;
if (big < temp) big = temp;
}
/* compute the absolute tolerance eps used to skip small entries
of the column */
if (!(0.0 < tol && tol < 1.0))
xfault("lpx_prim_ratio_test: tol = %g; invalid tolerance\n",
tol);
eps = tol * (1.0 + big);
/* initial settings */
p = 0, teta = DBL_MAX, big = 0.0;
/* walk through the entries of the specified column */
for (t = 1; t <= len; t++)
{ /* get the ordinal number of basic variable */
k = ind[t];
if (!(1 <= k && k <= m+n))
xfault("lpx_prim_ratio_test: ind[%d] = %d; variable number "
"out of range\n", t, k);
if (k <= m)
tagx = lpx_get_row_stat(lp, k);
else
tagx = lpx_get_col_stat(lp, k-m);
if (tagx != LPX_BS)
xfault("lpx_prim_ratio_test: ind[%d] = %d; non-basic variab"
"le not allowed\n", t, k);
/* determine index of the variable x[k] in the vector xB */
if (k <= m)
i = lpx_get_row_b_ind(lp, k);
else
i = lpx_get_col_b_ind(lp, k-m);
xassert(1 <= i && i <= m);
/* determine unscaled bounds and value of the basic variable
xB[i] in the current basic solution */
if (k <= m)
{ typx = lpx_get_row_type(lp, k);
lb_i = lpx_get_row_lb(lp, k);
ub_i = lpx_get_row_ub(lp, k);
bbar_i = lpx_get_row_prim(lp, k);
}
else
{ typx = lpx_get_col_type(lp, k-m);
lb_i = lpx_get_col_lb(lp, k-m);
ub_i = lpx_get_col_ub(lp, k-m);
bbar_i = lpx_get_col_prim(lp, k-m);
}
/* determine influence coefficient for the basic variable
x[k] = xB[i] in the explicitly specified column and turn to
the case of increasing the variable y in order to simplify
the program logic */
alfa_i = (how > 0 ? +val[t] : -val[t]);
abs_alfa_i = (alfa_i > 0.0 ? +alfa_i : -alfa_i);
/* analyze main cases */
switch (typx)
{ case LPX_FR:
/* xB[i] is free variable */
continue;
case LPX_LO:
lo: /* xB[i] has an lower bound */
if (alfa_i > - eps) continue;
temp = (lb_i - bbar_i) / alfa_i;
break;
case LPX_UP:
up: /* xB[i] has an upper bound */
if (alfa_i < + eps) continue;
temp = (ub_i - bbar_i) / alfa_i;
break;
case LPX_DB:
/* xB[i] has both lower and upper bounds */
if (alfa_i < 0.0) goto lo; else goto up;
case LPX_FX:
/* xB[i] is fixed variable */
if (abs_alfa_i < eps) continue;
temp = 0.0;
break;
default:
xassert(typx != typx);
}
/* if the value of the variable xB[i] violates its lower or
upper bound (slightly, because the current basis is assumed
to be primal feasible), temp is negative; we can think this
happens due to round-off errors and the value is exactly on
the bound; this allows replacing temp by zero */
if (temp < 0.0) temp = 0.0;
/* apply the minimal ratio test */
if (teta > temp || teta == temp && big < abs_alfa_i)
p = k, teta = temp, big = abs_alfa_i;
}
/* return the ordinal number of the chosen basic variable */
return p;
}
