State¶
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class State¶
A State object records a snapshot of the current state of a simulation at a point in time. You create it by calling getState() on a Context.
When a State is created, you specify what information should be stored in it. This saves time and memory by only copying in the information that you actually want. This is especially important for forces and energies, since they may need to be calculated. If you query a State object for a piece of information which is not available (because it was not requested when the State was created), it will throw an exception.
Public Types
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enum DataType¶
This is an enumeration of the types of data which may be stored in a State. When you create a State, use these values to specify which data types it should contain.
Values:
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enumerator Positions¶
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enumerator Velocities¶
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enumerator Forces¶
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enumerator Energy¶
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enumerator Parameters¶
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enumerator ParameterDerivatives¶
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enumerator IntegratorParameters¶
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enumerator Positions¶
Public Functions
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State()¶
Construct an empty State containing no data. This exists so State objects can be used in STL containers.
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long long getStepCount() const¶
Get the number of integration steps that had been performed when this State was created.
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const std::vector<Vec3> &getPositions() const¶
Get the position of each particle. If this State does not contain positions, this will throw an exception.
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const std::vector<Vec3> &getVelocities() const¶
Get the velocity of each particle. If this State does not contain velocities, this will throw an exception.
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const std::vector<Vec3> &getForces() const¶
Get the force acting on each particle. If this State does not contain forces, this will throw an exception.
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double getKineticEnergy() const¶
Get the total kinetic energy of the system. If this State does not contain energies, this will throw an exception.
Note that this may be different from simply mv2/2 summed over all particles. For example, a leapfrog integrator will store velocities offset by half a step, so they must be adjusted before computing the kinetic energy. This routine returns the kinetic energy at the current time, computed in a way that is appropriate for whatever Integrator is being used.
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double getPotentialEnergy() const¶
Get the total potential energy of the system. If this State does not contain energies, this will throw an exception.
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void getPeriodicBoxVectors(Vec3 &a, Vec3 &b, Vec3 &c) const¶
Get the vectors defining the axes of the periodic box (measured in nm).
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a – [out] the vector defining the first edge of the periodic box
b – [out] the vector defining the second edge of the periodic box
c – [out] the vector defining the third edge of the periodic box
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double getPeriodicBoxVolume() const¶
Get the volume of the periodic box (measured in nm^3).
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const std::map<std::string, double> &getParameters() const¶
Get a map containing the values of all parameters. If this State does not contain parameters, this will throw an exception.
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const std::map<std::string, double> &getEnergyParameterDerivatives() const¶
Get a map containing derivatives of the potential energy with respect to context parameters. In most cases derivatives are only calculated if the corresponding Force objects have been specifically told to compute them. Otherwise, the values in the map will be zero. Likewise, if multiple Forces depend on the same parameter but only some have been told to compute derivatives with respect to it, the returned value will include only the contributions from the Forces that were told to compute it.
If this State does not contain parameter derivatives, this will throw an exception.
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enum DataType¶
