# HarmonicAngleForce Class Reference

This class implements an interaction between groups of three particles that varies harmonically with the angle between them. More...

`#include <HarmonicAngleForce.h>`

Inheritance diagram for HarmonicAngleForce:

List of all members.

## Classes
class | AngleInfo
| This is an internal class used to record information about an angle.
## Public Member Functions
| HarmonicAngleForce ()
| Create a HarmonicAngleForce.
int | getNumAngles () const
| Get the number of harmonic bond angle terms in the potential function.
int | addAngle (int particle1, int particle2, int particle3, double angle, double k)
| Add an angle term to the force field.
void | getAngleParameters (int index, int &particle1, int &particle2, int &particle3, double &angle, double &k) const
| Get the force field parameters for an angle term.
void | setAngleParameters (int index, int particle1, int particle2, int particle3, double angle, double k)
| Set the force field parameters for an angle term.
void | updateParametersInContext (Context &context)
| Update the per-angle parameters in a Context to match those stored in this Force object.
## Protected Member Functions
ForceImpl * | createImpl () const
| When a Context is created, it invokes this method on each Force in the System.

## Detailed Description

This class implements an interaction between groups of three particles that varies harmonically with the angle between them.

To use it, create a HarmonicAngleForce object then call addAngle() once for each angle. After an angle has been added, you can modify its force field parameters by calling setAngleParameters(). This will have no effect on Contexts that already exist unless you call updateParametersInContext().

## Constructor & Destructor Documentation

HarmonicAngleForce | ( |  | ) |

Create a HarmonicAngleForce.

## Member Function Documentation

int addAngle | ( | int | particle1,
|  | int | particle2,
|  | int | particle3,
|  | double | angle,
|  | double | k |
| ) |  |  |

Add an angle term to the force field.

Parameters:

  | particle1 | the index of the first particle forming the angle
  | particle2 | the index of the second particle forming the angle
  | particle3 | the index of the third particle forming the angle
  | angle | the equilibrium angle, measured in radians
  | k | the harmonic force constant for the angle, measured in kJ/mol/radian^2

Returns:
  the index of the angle that was added

ForceImpl* createImpl | ( |  | ) | const`[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.

void getAngleParameters | ( | int | index,
|  | int & | particle1,
|  | int & | particle2,
|  | int & | particle3,
|  | double & | angle,
|  | double & | k |
| ) |  |  | const

Get the force field parameters for an angle term.

Parameters:

  | index | the index of the angle for which to get parameters
  | particle1 | the index of the first particle forming the angle
  | particle2 | the index of the second particle forming the angle
  | particle3 | the index of the third particle forming the angle
  | angle | the equilibrium angle, measured in radians
  | k | the harmonic force constant for the angle, measured in kJ/mol/radian^2

int getNumAngles | ( |  | ) | const`[inline]`

Get the number of harmonic bond angle terms in the potential function.

void setAngleParameters | ( | int | index,
|  | int | particle1,
|  | int | particle2,
|  | int | particle3,
|  | double | angle,
|  | double | k |
| ) |  |  |

Set the force field parameters for an angle term.

Parameters:

  | index | the index of the angle for which to set parameters
  | particle1 | the index of the first particle forming the angle
  | particle2 | the index of the second particle forming the angle
  | particle3 | the index of the third particle forming the angle
  | angle | the equilibrium angle, measured in radians
  | k | the harmonic force constant for the angle, measured in kJ/mol/radian^2

void updateParametersInContext | ( | Context & | context | ) |

Update the per-angle parameters in a Context to match those stored in this Force object.

This method provides an efficient method to update certain parameters in an existing Context without needing to reinitialize it. Simply call setAngleParameters() to modify this object's parameters, then call updateParametersInState() to copy them over to the Context.

The only information this method updates is the values of per-angle parameters. The set of particles involved in a angle cannot be changed, nor can new angles be added.

The documentation for this class was generated from the following file:

- HarmonicAngleForce.h