void
HeuristicInnerApproximation::extractInnerApproximation(OsiTMINLPInterface & nlp, OsiSolverInterface &si,
const double * x, bool getObj) {
int n;
int m;
int nnz_jac_g;
int nnz_h_lag;
Ipopt::TNLP::IndexStyleEnum index_style;
TMINLP2TNLP * problem = nlp.problem();
//Get problem information
problem->get_nlp_info(n, m, nnz_jac_g, nnz_h_lag, index_style);
vector<int> jRow(nnz_jac_g);
vector<int> jCol(nnz_jac_g);
vector<double> jValues(nnz_jac_g);
problem->eval_jac_g(n, NULL, 0, m, nnz_jac_g, jRow(), jCol(), NULL);
if(index_style == Ipopt::TNLP::FORTRAN_STYLE)//put C-style
{
for(int i = 0 ; i < nnz_jac_g ; i++){
jRow[i]--;
jCol[i]--;
}
}
//get Jacobian
problem->eval_jac_g(n, x, 1, m, nnz_jac_g, NULL, NULL,
jValues());
vector<double> g(m);
problem->eval_g(n, x, 1, m, g());
vector<int> nonLinear(m);
//store non linear constraints (which are to be removed from IA)
int numNonLinear = 0;
const double * rowLower = nlp.getRowLower();
const double * rowUpper = nlp.getRowUpper();
const double * colLower = nlp.getColLower();
const double * colUpper = nlp.getColUpper();
assert(m == nlp.getNumRows());
double infty = si.getInfinity();
double nlp_infty = nlp.getInfinity();
vector<Ipopt::TNLP::LinearityType> constTypes(m);
problem->get_constraints_linearity(m, constTypes());
for (int i = 0; i < m; i++) {
if (constTypes[i] == Ipopt::TNLP::NON_LINEAR) {
nonLinear[numNonLinear++] = i;
}
}
vector<double> rowLow(m - numNonLinear);
vector<double> rowUp(m - numNonLinear);
int ind = 0;
for (int i = 0; i < m; i++) {
if (constTypes[i] != Ipopt::TNLP::NON_LINEAR) {
if (rowLower[i] > -nlp_infty) {
// printf("Lower %g ", rowLower[i]);
rowLow[ind] = (rowLower[i]);
} else
rowLow[ind] = -infty;
if (rowUpper[i] < nlp_infty) {
// printf("Upper %g ", rowUpper[i]);
rowUp[ind] = (rowUpper[i]);
} else
rowUp[ind] = infty;
ind++;
}
}
CoinPackedMatrix mat(true, jRow(), jCol(), jValues(), nnz_jac_g);
mat.setDimensions(m, n); // In case matrix was empty, this should be enough
//remove non-linear constraints
mat.deleteRows(numNonLinear, nonLinear());
int numcols = nlp.getNumCols();
vector<double> obj(numcols);
for (int i = 0; i < numcols; i++)
obj[i] = 0.;
si.loadProblem(mat, nlp.getColLower(), nlp.getColUpper(),
obj(), rowLow(), rowUp());
const Bonmin::TMINLP::VariableType* variableType = problem->var_types();
for (int i = 0; i < n; i++) {
if ((variableType[i] == TMINLP::BINARY) || (variableType[i]
== TMINLP::INTEGER))
si.setInteger(i);
}
if (getObj) {
bool addObjVar = false;
if (problem->hasLinearObjective()) {
double zero;
vector<double> x0(n, 0.);
problem->eval_f(n, x0(), 1, zero);
si.setDblParam(OsiObjOffset, -zero);
//Copy the linear objective and don't create a dummy variable.
problem->eval_grad_f(n, x, 1, obj());
si.setObjective(obj());
} else {
addObjVar = true;
}
if (addObjVar) {
nlp.addObjectiveFunction(si, x);
}
}
// Hassan IA initial description
int InnerDesc = 1;
if (InnerDesc == 1) {
OsiCuts cs;
double * p = CoinCopyOfArray(colLower, n);
double * pp = CoinCopyOfArray(colLower, n);
double * up = CoinCopyOfArray(colUpper, n);
const int& nbAp = nbAp_;
std::vector<int> nbG(m, 0);// Number of generated points for each nonlinear constraint
std::vector<double> step(n);
for (int i = 0; i < n; i++) {
if (colUpper[i] > 1e08) {
up[i] = 0;
}
if (colUpper[i] > 1e08 || colLower[i] < -1e08 || (variableType[i]
== TMINLP::BINARY) || (variableType[i] == TMINLP::INTEGER)) {
step[i] = 0;
} else
step[i] = (up[i] - colLower[i]) / (nbAp);
if (colLower[i] < -1e08) {
p[i] = 0;
pp[i] = 0;
}
}
vector<double> g_p(m);
vector<double> g_pp(m);
for (int j = 1; j <= nbAp; j++) {
for (int i = 0; i < n; i++) {
pp[i] += step[i];
}
problem->eval_g(n, p, 1, m, g_p());
problem->eval_g(n, pp, 1, m, g_pp());
double diff = 0;
int varInd = 0;
for (int i = 0; (i < m && constTypes[i] == Ipopt::TNLP::NON_LINEAR); i++) {
if (varInd == n - 1)
varInd = 0;
diff = std::abs(g_p[i] - g_pp[i]);
if (nbG[i] < nbAp - 1) {
getMyInnerApproximation(nlp, cs, i, p, pp);// Generate a chord connecting the two points
p[varInd] = pp[varInd];
nbG[i]++;
}
varInd++;
}
}
for(int i = 0; (i< m && constTypes[i] == Ipopt::TNLP::NON_LINEAR); i++) {
// getConstraintOuterApproximation(cs, i, colUpper, NULL, true);// Generate Tangents at current point
getMyInnerApproximation(nlp, cs, i, p, up);// Generate a chord connecting the two points
}
delete [] p;
delete [] pp;
delete [] up;
si.applyCuts(cs);
}
}
/** Get an inner-approximation constraint obtained by drawing a chord linking the two given points x and x2.
* This only applies to nonlinear constraints featuring univariate functions (f(x) <= y).**/
bool
HeuristicInnerApproximation::getMyInnerApproximation(OsiTMINLPInterface &si, OsiCuts &cs, int ind,
const double * x, const double * x2) {
int n, m, nnz_jac_g, nnz_h_lag;
Ipopt::TNLP::IndexStyleEnum index_style;
TMINLP2TNLP * problem = si.problem();
problem->get_nlp_info(n, m, nnz_jac_g, nnz_h_lag, index_style);
CoinPackedVector cut;
double lb = 0;
double ub = 0;
double infty = si.getInfinity();
lb = -infty; // we only compute <= constraints
double g = 0;
double g2 = 0;
double diff = 0;
double a = 0;
problem->eval_gi(n, x, 1, ind, g);
problem->eval_gi(n, x2, 1, ind, g2);
vector<int> jCol(n);
int nnz;
problem->eval_grad_gi(n, x2, 0, ind, nnz, jCol(), NULL);
vector<double> jValues(nnz);
problem->eval_grad_gi(n, x2, 0, ind, nnz, NULL, jValues());
bool add = false;
for (int i = 0; i < nnz; i++) {
const int &colIdx = jCol[i];
if(index_style == Ipopt::TNLP::FORTRAN_STYLE) jCol[i]--;
diff = x[colIdx] - x2[colIdx];
if (fabs(diff) >= 1e-8) {
a = (g - g2) / diff;
cut.insert(colIdx, a);
ub = a * x[colIdx] - g;
add = true;
} else
cut.insert(colIdx, jValues[i]);
}
if (add) {
OsiRowCut newCut;
newCut.setGloballyValidAsInteger(1);
newCut.setLb(lb);
//********* Perspective Extension ********//
int* ids = problem->get_const_xtra_id(); // vector of indices corresponding to the binary variable activating the corresponding constraint
int binary_id = (ids == NULL) ? -1 : ids[ind]; // Get the index of the corresponding indicator binary variable
if(binary_id>0) {// If this hyperplane is a linearization of a disjunctive constraint, we link its righthand side to the corresponding indicator binary variable
cut.insert(binary_id, -ub); // ∂x ≤ ub => ∂x - ub*z ≤ 0
newCut.setUb(0);
}
else
newCut.setUb(ub);
//********* Perspective Extension ********//
newCut.setRow(cut);
cs.insert(newCut);
return true;
}
return false;
}
