void optimize()
{
if (use_selection)
{
Log.info() << "SELECT: " << selection << endl;
Selector selector(selection);
S.apply(selector);
// count selected vs. unselected atoms
Size selected = 0;
AtomConstIterator ai = S.beginAtom();
for (; +ai; ++ai)
{
selected += (ai->isSelected() ? 1 : 0);
}
Log.info() << "selected " << selected << " out of " << S.countAtoms() << " atoms." << endl;
}
// minimize
Log.info() << "starting minimization";
EnergyMinimizer* minimizer;
if (sd_minimizer)
{
minimizer = new SteepestDescentMinimizer(amber);
}
else
{
minimizer = new ConjugateGradientMinimizer(amber);
}
if (verbose)
{
minimizer->setEnergyOutputFrequency(1);
}
else
{
minimizer->setEnergyOutputFrequency(20);
}
minimizer->setEnergyDifferenceBound(1e-9);
minimizer->setMaxSameEnergy(20);
minimizer->setMaxGradient(max_gradient);
minimizer->minimize(max_iterations);
Log.info() << "minimization complete" << endl;
Log.info() << "final gradient: " << amber.getRMSGradient() << " kJ/mol A" << endl;
S.deselect();
amber.updateEnergy();
Log.info() << "final energy: " << amber.getEnergy() << " kJ/mol" << endl;
// dump the minimizer and force field options
// for documentation purposes
amber.options.dump(Log);
minimizer->options.dump(Log);
Log.info() << "done." << endl;
}
int main(int argc, char** argv)
{
Log.setPrefix(cout, "[%T] ");
Log.setPrefix(cerr, "[%T] ERROR: ");
// issue a usage hint if called without parameters
if (argc != 3)
{
Log << argv[0] << " <PDB infile> <PDB outfile>" << endl;
return 1;
}
// open a PDB file with the name of the first argument
PDBFile file(argv[1]);
if (!file)
{
// if file does not exist: complain and abort
Log.error() << "error opening " << argv[1] << " for input." << endl;
return 2;
}
// create a system and read the contents of the PDB file
System S;
file >> S;
file.close();
// print the number of atoms read from the file
Log << "read " << S.countAtoms() << " atoms." << endl;
// now we open a fragment database
Log << "reading fragment DB..." << endl;
FragmentDB fragment_db("");
// and normalize the atom names, i.e. we convert different
// naming standards to the PDB naming scheme - just in case!
Log << "normalizing names..." << endl;
S.apply(fragment_db.normalize_names);
// now we add any missing hydrogens to the residues
// the data on the hydrogen positions stems from the
// fragment database. However the hydrogen positions
// created in this way are only good estimates
Log << "creating missing atoms..." << endl;
S.apply(fragment_db.add_hydrogens);
Log << "added " << fragment_db.add_hydrogens.getNumberOfInsertedAtoms()
<< " atoms" << endl;
// now we create the bonds between the atoms (PDB files hardly
// ever contain a complete set of CONECT records)
Log << "building bonds..." << endl;
S.apply(fragment_db.build_bonds);
// now we check whether the model we built is consistent
// The ResidueChecker checks for charges, bond lengths,
// and missing atoms
Log << "checking the built model..." << endl;
ResidueChecker checker(fragment_db);
S.apply(checker);
// now we create an AMBER force field
Log << "setting up force field..." << endl;
AmberFF FF;
// we then select all hydrogens (element(H))
// using a specialized processor (Selector)
S.deselect();
FF.setup(S);
Selector selector("element(H)");
S.apply(selector);
// just for curiosity: check how many atoms we are going
// to optimize
Log << "optimizing " << FF.getNumberOfMovableAtoms() << " out of " << S.countAtoms() << " atoms" << endl;
// now we create a minimizer object that uses a conjugate
// gradient algorithm to optimize the atom positions
ConjugateGradientMinimizer minimizer;
// calculate the total energy of the system
float initial_energy = FF.updateEnergy();
Log << "initial energy: " << initial_energy << " kJ/mol" << endl;
// initialize the minimizer and perform (up to)
// 1000 optimization steps
minimizer.setup(FF);
minimizer.setEnergyOutputFrequency(1);
minimizer.minimize(50);
// calculate the terminal energy and print it
float terminal_energy = FF.getEnergy();
Log << "energy before/after minimization: " << initial_energy << "/" << terminal_energy << " kJ/mol" << endl;
// write the optimized structure to a file whose
// name is given as the second command line argument
Log << "writing PBD file " << argv[2] << endl;
file.open(argv[2], ios::out);
file << S;
file.close();
// done.
return 0;
}
