CustomExternalForce Class Reference

This class implements an "external" force on particles. More...

Inheritance diagram for CustomExternalForce:
Force

List of all members.

Public Member Functions

def getNumParticles
 getNumParticles(self) -> int
def getNumPerParticleParameters
 getNumPerParticleParameters(self) -> int
def getNumGlobalParameters
 getNumGlobalParameters(self) -> int
def getEnergyFunction
 getEnergyFunction(self) -> string
def setEnergyFunction
 setEnergyFunction(self, string energy)
def addPerParticleParameter
 addPerParticleParameter(self, string name) -> int
def getPerParticleParameterName
 getPerParticleParameterName(self, int index) -> string
def setPerParticleParameterName
 setPerParticleParameterName(self, int index, string name)
def addGlobalParameter
 addGlobalParameter(self, string name, double defaultValue) -> int
def getGlobalParameterName
 getGlobalParameterName(self, int index) -> string
def setGlobalParameterName
 setGlobalParameterName(self, int index, string name)
def getGlobalParameterDefaultValue
 getGlobalParameterDefaultValue(self, int index) -> double
def setGlobalParameterDefaultValue
 setGlobalParameterDefaultValue(self, int index, double defaultValue)
def addParticle
 addParticle(self, int particle, vectord parameters) -> int
def getParticleParameters
 getParticleParameters(self, int index)
def setParticleParameters
 setParticleParameters(self, int index, int particle, vectord parameters)
def __init__
 __init__(self, string energy) -> CustomExternalForce __init__(self, CustomExternalForce other) -> CustomExternalForce
def __del__
 __del__(self)

Public Attributes

 this

Detailed Description

This class implements an "external" force on particles.

The force may be applied to any subset of the particles in the System. The force on each particle is specified by an arbitrary algebraic expression, which may depend on the current position of the particle as well as on arbitrary global and per-particle parameters.

To use this class, create a CustomExternalForce object, passing an algebraic expression to the constructor that defines the potential energy of each affected particle. The expression may depend on the particle's x, y, and z coordinates, as well as on any parameters you choose. Then call addPerParticleParameter() to define per-particle parameters, and addGlobalParameter() to define global parameters. The values of per-particle parameters are specified as part of the system definition, while values of global parameters may be modified during a simulation by calling Context.setParameter(). Finally, call addParticle() once for each particle that should be affected by the force. After a particle has been added, you can modify its parameters by calling setParticleParameters().

As an example, the following code creates a CustomExternalForce that attracts each particle to a target position (x0, y0, z0) via a harmonic potential:

CustomExternalForce* force = new CustomExternalForce("k*((x-x0)^2+(y-y0)^2+(z-z0)^2)");

This force depends on four parameters: the spring constant k and equilibrium coordinates x0, y0, and z0. The following code defines these parameters:

     force->addGlobalParameter("k");
     force->addPerParticleParameter("x0");
     force->addPerParticleParameter("y0");
     force->addPerParticleParameter("z0");

Expressions may involve the operators + (add), - (subtract), * (multiply), / (divide), and ^ (power), and the following functions: sqrt, exp, log, sin, cos, sec, csc, tan, cot, asin, acos, atan, sinh, cosh, tanh, erf, erfc, min, max, abs, step. All trigonometric functions are defined in radians, and log is the natural logarithm. step(x) = 0 if x is less than 0, 1 otherwise.

Member Function Documentation

def __del__ (   self  ) 

__del__(self)

Reimplemented from Force.

def __init__ (   self,
  args 
)

__init__(self, string energy) -> CustomExternalForce __init__(self, CustomExternalForce other) -> CustomExternalForce

Create a CustomExternalForce.

Parameters:
energy an algebraic expression giving the potential energy of each particle as a function of its x, y, and z coordinates
def addGlobalParameter (   self,
  args 
)

addGlobalParameter(self, string name, double defaultValue) -> int

Add a new global parameter that the force may depend on.

Parameters:
name the name of the parameter
defaultValue the default value of the parameter
def addParticle (   self,
  args 
)

addParticle(self, int particle, vectord parameters) -> int

Add a particle term to the force field.

Parameters:
particle the index of the particle this term is applied to
parameters the list of parameters for the new force term
def addPerParticleParameter (   self,
  args 
)

addPerParticleParameter(self, string name) -> int

Add a new per-particle parameter that the force may depend on.

Parameters:
name the name of the parameter
def getEnergyFunction (   self  ) 

getEnergyFunction(self) -> string

Get the algebraic expression that gives the potential energy of each particle

def getGlobalParameterDefaultValue (   self,
  args 
)

getGlobalParameterDefaultValue(self, int index) -> double

Get the default value of a global parameter.

Parameters:
index the index of the parameter for which to get the default value
def getGlobalParameterName (   self,
  args 
)

getGlobalParameterName(self, int index) -> string

Get the name of a global parameter.

Parameters:
index the index of the parameter for which to get the name
def getNumGlobalParameters (   self  ) 

getNumGlobalParameters(self) -> int

Get the number of global parameters that the force depends on.

def getNumParticles (   self  ) 

getNumParticles(self) -> int

Get the number of particles for which force field parameters have been defined.

def getNumPerParticleParameters (   self  ) 

getNumPerParticleParameters(self) -> int

Get the number of per-particle parameters that the force depends on

def getParticleParameters (   self,
  args 
)

getParticleParameters(self, int index)

Get the force field parameters for a force field term.

Parameters:
index the index of the particle term for which to get parameters
particle the index of the particle this term is applied to
parameters the list of parameters for the force field term
def getPerParticleParameterName (   self,
  args 
)

getPerParticleParameterName(self, int index) -> string

Get the name of a per-particle parameter.

Parameters:
index the index of the parameter for which to get the name
def setEnergyFunction (   self,
  args 
)

setEnergyFunction(self, string energy)

Set the algebraic expression that gives the potential energy of each particle

def setGlobalParameterDefaultValue (   self,
  args 
)

setGlobalParameterDefaultValue(self, int index, double defaultValue)

Set the default value of a global parameter.

Parameters:
index the index of the parameter for which to set the default value
name the default value of the parameter
def setGlobalParameterName (   self,
  args 
)

setGlobalParameterName(self, int index, string name)

Set the name of a global parameter.

Parameters:
index the index of the parameter for which to set the name
name the name of the parameter
def setParticleParameters (   self,
  args 
)

setParticleParameters(self, int index, int particle, vectord parameters)

Set the force field parameters for a force field term.

Parameters:
index the index of the particle term for which to set parameters
particle the index of the particle this term is applied to
parameters the list of parameters for the force field term
def setPerParticleParameterName (   self,
  args 
)

setPerParticleParameterName(self, int index, string name)

Set the name of a per-particle parameter.

Parameters:
index the index of the parameter for which to set the name
name the name of the parameter

Member Data Documentation

this
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