Object gen fixed seed

src/io/MultiObjectGenerator.cpp

@@ -9,7 +9,9 @@
 #include <mpi.h>
 #endif
 
+#include "IOHelpers.h"
 #include "Domain.h"
+#include "Simulation.h"
 #include "ensemble/EnsembleBase.h"
 #include "io/ObjectGenerator.h"
 #include "molecules/MoleculeIdPool.h"
@@ -41,6 +43,7 @@ void MultiObjectGenerator::readXML(XMLfileUnits& xmlconfig) {
 		_generators.push_back(generator);
 	}
 	xmlconfig.changecurrentnode(oldpath);
+	xmlconfig.getNodeValue("removeDrift", _removeDrift);
 }
 
 
@@ -55,6 +58,8 @@ unsigned long MultiObjectGenerator::readPhaseSpace(ParticleContainer* particleCo
 		numMolecules += generator->readPhaseSpace(particleContainer, domain, domainDecomp);
 	}
 	particleContainer->updateMoleculeCaches();
+	if(_removeDrift)
+		IOHelpers::removeMomentum(particleContainer, *(global_simulation->getEnsemble()->getComponents()), domainDecomp);
 	Log::global_log->info() << "Number of locally inserted molecules: " << numMolecules << std::endl;
 	_globalNumMolecules = numMolecules;
 #ifdef ENABLE_MPI

src/io/MultiObjectGenerator.h

@@ -18,13 +18,18 @@ class MultiObjectGenerator : public InputBase {
 
 	/** @brief Read in XML configuration for Generator and all its included objects.
 	 *
+	 * The removeDrift parameter uses the function IOHelpers::removeMomentum() to remove overall drift from the 
+	 * phasespace after initialisation, similar to what is done in CubicGridGenerator. This is off by default, as
+	 * some experiments may want to load checkpoints with initial drift.
+	 * 
 	 * The following xml object structure is handled by this method:
 	 * @note This structure is not fixed yet and may see changes
 	 * \code{.xml}
 	   <generator name="MultiObjectGenerator">
 	     <objectgenerator> <!-- ... --> </objectgenerator>
 	     ...
 	     <velocityAssigner> <!-- ... --> </velocityAssigner>
+		 <removeDrift>BOOL</removeDrift>
 	   </generator >
 	   \endcode
 	 */
@@ -38,6 +43,7 @@ class MultiObjectGenerator : public InputBase {
 
 	std::list<ObjectGenerator*> _generators;
 	unsigned long _globalNumMolecules;
+	bool _removeDrift = false;
 };
 
 #endif  // SRC_IO_MULTIOBJECTGENERATOR_H_

src/io/ObjectGenerator.cpp

@@ -66,6 +66,13 @@ void ObjectGenerator::readXML(XMLfileUnits& xmlconfig) {
 		const long seed = [&]() -> long {
 			bool enableRandomSeed = false;
 			xmlconfig.getNodeValue("@enableRandomSeed", enableRandomSeed);
+			long fixedSeed = 0;
+			xmlconfig.getNodeValue("@seed", fixedSeed);
+			if (fixedSeed != 0 && enableRandomSeed) {
+				std::ostringstream error_message;
+				error_message << "Cannot simultaneously have a simulation seed and a random seed!" << std::endl;
+				MARDYN_EXIT(error_message.str());
+			}
 			if(enableRandomSeed) {
 				/** A random seed for the velocity generator is created.
 				 *  The current rank is added to make sure that, if multiple simulations are instantiated across
@@ -74,7 +81,9 @@ void ObjectGenerator::readXML(XMLfileUnits& xmlconfig) {
 				 */
 				return std::chrono::system_clock::now().time_since_epoch().count() + _simulation.domainDecomposition().getRank();
 
-			} else {
+			} else if(fixedSeed != 0) {
+				return fixedSeed + _simulation.domainDecomposition().getRank();
+			} else { // if the seed is zero, maintain old behaviour
 				return 0;
 			}
 		}();

src/io/ObjectGenerator.h

@@ -24,14 +24,19 @@ class ObjectGenerator : public InputBase {
 	ObjectGenerator() : _filler(nullptr), _object(nullptr), _velocityAssigner(nullptr), _moleculeIdPool(nullptr) {};
 
 	/** @brief Read in XML configuration for ObjectGenerator and all its included objects.
+	 * 
+	 * The velocityAssigner can take two additional parameters. enableRandomSeed adds the option of having random
+	 * intial molecule velocities at the beginning of the simulation. If a seed is specified, that value is used
+	 * instead. Leaving both blank gives the default behaviour (seed = 0). Both cannot be nonzero simultaneously.
 	 *
 	 * The following XML object structure is handled by this method:
 	 * @note This structure is not fixed yet and may see changes
 	 * \code{.xml}
 	   <objectgenerator>
 	     <filler type="STRING"> <!-- see Filler documentation --> </filler>
 	     <object type="STRING"> <!-- see Object documentation --> </object>
-	     <velocityAssigner type="STRING"> <!-- see VelocityAssignerBase documentation --> </velocityAssigner>
+	     <velocityAssigner type="STRING" enableRandomSeed="BOOL" seed="LONG"> 
+			<!-- see VelocityAssignerBase documentation --> </velocityAssigner>
 	   </objectgenerator>
 	   \endcode
 	 */