CustomExternalForce Class Reference
This class implements an "external" force on particles.
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#include <CustomExternalForce.h>
List of all members.
Classes |
class | GlobalParameterInfo |
| This is an internal class used to record information about a global parameter.
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class | ParticleInfo |
| This is an internal class used to record information about a particle.
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class | ParticleParameterInfo |
| This is an internal class used to record information about a per-particle parameter.
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Public Member Functions |
| CustomExternalForce (const std::string &energy) |
| Create a CustomExternalForce.
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int | getNumParticles () const |
| Get the number of particles for which force field parameters have been defined.
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int | getNumPerParticleParameters () const |
| Get the number of per-particle parameters that the force depends on.
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int | getNumGlobalParameters () const |
| Get the number of global parameters that the force depends on.
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const std::string & | getEnergyFunction () const |
| Get the algebraic expression that gives the potential energy of each particle.
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void | setEnergyFunction (const std::string &energy) |
| Set the algebraic expression that gives the potential energy of each particle.
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int | addPerParticleParameter (const std::string &name) |
| Add a new per-particle parameter that the force may depend on.
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const std::string & | getPerParticleParameterName (int index) const |
| Get the name of a per-particle parameter.
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void | setPerParticleParameterName (int index, const std::string &name) |
| Set the name of a per-particle parameter.
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int | addGlobalParameter (const std::string &name, double defaultValue) |
| Add a new global parameter that the force may depend on.
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const std::string & | getGlobalParameterName (int index) const |
| Get the name of a global parameter.
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void | setGlobalParameterName (int index, const std::string &name) |
| Set the name of a global parameter.
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double | getGlobalParameterDefaultValue (int index) const |
| Get the default value of a global parameter.
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void | setGlobalParameterDefaultValue (int index, double defaultValue) |
| Set the default value of a global parameter.
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int | addParticle (int particle, const std::vector< double > ¶meters) |
| Add a particle term to the force field.
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void | getParticleParameters (int index, int &particle, std::vector< double > ¶meters) const |
| Get the force field parameters for a force field term.
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void | setParticleParameters (int index, int particle, const std::vector< double > ¶meters) |
| Set the force field parameters for a force field term.
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Protected Member Functions |
ForceImpl * | createImpl () |
| When a Context is created, it invokes this method on each Force in the System.
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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.
Constructor & Destructor Documentation
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 |
Member Function Documentation
int addGlobalParameter |
( |
const std::string & |
name, |
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double |
defaultValue | |
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) |
| | |
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 |
- Returns:
- the index of the parameter that was added
int addParticle |
( |
int |
particle, |
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const std::vector< double > & |
parameters | |
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) |
| | |
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 |
- Returns:
- the index of the particle term that was added
int addPerParticleParameter |
( |
const std::string & |
name |
) |
|
Add a new per-particle parameter that the force may depend on.
- Parameters:
-
| name | the name of the parameter |
- Returns:
- the index of the parameter that was added
ForceImpl* createImpl |
( |
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) |
[protected, virtual] |
When a Context is created, it invokes this method on each Force in the System.
It should create a new ForceImpl object which can be used by the context for calculating forces. The ForceImpl will be deleted automatically when the Context is deleted.
Implements Force.
const std::string& getEnergyFunction |
( |
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) |
const |
Get the algebraic expression that gives the potential energy of each particle.
double getGlobalParameterDefaultValue |
( |
int |
index |
) |
const |
Get the default value of a global parameter.
- Parameters:
-
| index | the index of the parameter for which to get the default value |
- Returns:
- the parameter default value
const std::string& getGlobalParameterName |
( |
int |
index |
) |
const |
Get the name of a global parameter.
- Parameters:
-
| index | the index of the parameter for which to get the name |
- Returns:
- the parameter name
int getNumGlobalParameters |
( |
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) |
const [inline] |
Get the number of global parameters that the force depends on.
int getNumParticles |
( |
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) |
const [inline] |
Get the number of particles for which force field parameters have been defined.
int getNumPerParticleParameters |
( |
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) |
const [inline] |
Get the number of per-particle parameters that the force depends on.
void getParticleParameters |
( |
int |
index, |
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int & |
particle, |
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std::vector< double > & |
parameters | |
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) |
| | const |
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 |
const std::string& getPerParticleParameterName |
( |
int |
index |
) |
const |
Get the name of a per-particle parameter.
- Parameters:
-
| index | the index of the parameter for which to get the name |
- Returns:
- the parameter name
void setEnergyFunction |
( |
const std::string & |
energy |
) |
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Set the algebraic expression that gives the potential energy of each particle.
void setGlobalParameterDefaultValue |
( |
int |
index, |
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double |
defaultValue | |
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) |
| | |
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 |
void setGlobalParameterName |
( |
int |
index, |
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const std::string & |
name | |
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) |
| | |
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 |
void setParticleParameters |
( |
int |
index, |
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int |
particle, |
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const std::vector< double > & |
parameters | |
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) |
| | |
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 |
void setPerParticleParameterName |
( |
int |
index, |
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const std::string & |
name | |
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) |
| | |
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 |
The documentation for this class was generated from the following file: