Constraint Class Reference

Constraints for optimization / dynamics. More...

#include <avogadro/core/constraint.h>

Public Types
enum	Type {   None = 0 ,   DistanceConstraint ,   AngleConstraint ,   TorsionConstraint ,   OutOfPlaneConstraint ,   UnknownConstraint }

Public Member Functions
	Constraint (Index a, Index b, Index c=MaxIndex, Index d=MaxIndex, Real value=0.0)
void	set (Index a, Index b, Index c=MaxIndex, Index d=MaxIndex, Real value=0.0)
void	setValue (Real value)
Real	value () const
std::tuple< Index, Index, Index, Index >	atoms () const
Index	aIndex () const
Index	bIndex () const
Index	cIndex () const
Index	dIndex () const
Real	k () const
void	setK (Real k)
Constraint::Type	type () const
bool	matches (Index a, Index b, Index c=MaxIndex, Index d=MaxIndex) const
bool	isValid (Index atomCount) const
bool	evaluate (const Array< Vector3 > &positions, Real &value) const
void	setType (Constraint::Type type) const

Static Public Attributes
static constexpr Real	DefaultDistanceK = 41840.0
static constexpr Real	DefaultAngularK = 10000.0

Protected Attributes
Index	m_aIndex = MaxIndex
Index	m_bIndex = MaxIndex
Index	m_cIndex = MaxIndex
Index	m_dIndex = MaxIndex
Real	m_value = 0.0
Real	m_k = DefaultDistanceK
bool	m_kSet = false
Constraint::Type	m_type = None
bool	m_typeExplicit = false

Detailed Description

Author

Geoffrey R. Hutchison

This class represents a distance, angle, or torsional constraint / restraint during optimization or dynamics. More technically, these are implemented as stiff harmonic oscillators restraining a particular atom set towards the value.

Distances are stored in Angstrom and angles / torsions in degrees, matching what the user sees in the property tables and constraint dialog. Energy calculators convert angular values to radians internally, so the angular force constants are in kJ/mol/radian^2.

Constructor & Destructor Documentation

Constraint()

Constraint	(	Index	a,
		Index	b,
		Index	c = MaxIndex,
		Index	d = MaxIndex,
		Real	value = 0.0 )

Constructor, results in a zero distance constraint

Parameters

a	Atom index of the first atom of the constraint
b	Atom index of the second atom of the constraint
c	Atom index of the third atom (for angles or torsions) or MaxIndex
d	Atom index of the fourth atom (for torsion constraints) or MaxIndex
value	The value of the constraint, either Angstrom for distance or degrees for angles and torsions

Member Function Documentation

set()

void set	(	Index	a,
		Index	b,
		Index	c = MaxIndex,
		Index	d = MaxIndex,
		Real	value = 0.0 )

Set the constraint

Parameters

a	Atom index of the first atom of the constraint
b	Atom index of the second atom of the constraint
c	Atom index of the third atom (for angles or torsions) or MaxIndex
d	Atom index of the fourth atom (for torsion constraints) or MaxIndex
value	The value of the constraint, either Angstrom for distance or degrees for angles and torsions

setValue()

void setValue

(

Real

value

)

Set the constraint value (distance, angle, dihedral)

Parameters

value

The value of the constraint, either Angstrom for distance or degrees for angles and torsions

value()

Real value

(

)

const

Returns

the constraint value

atoms()

std::tuple< Index, Index, Index, Index > atoms

(

)

const

Returns

the atoms in the constraint as a tuple

aIndex()

Index aIndex

(

)

const

Returns

the atom index from the constraint or MaxIndex

k()

Real k

(

)

const

Returns

the harmonic force constant, either kJ/mol/Angstrom^2 for a distance restraint or kJ/mol/radian^2 for an angular one. If no force constant has been set explicitly, a type-appropriate default is used – the two have different units and cannot share a value.

type()

Constraint::Type type

(

)

const

Returns

the type of constraint

matches()

bool matches	(	Index	a,
		Index	b,
		Index	c = MaxIndex,
		Index	d = MaxIndex ) const

Whether this constraint is on the coordinate the given atoms name. A coordinate read backwards is the same coordinate – the distance a-b is the distance b-a, and the torsion a-b-c-d is the torsion d-c-b-a – so both directions match. A table that lists a coordinate in its own order can then find the constraint on it however it happens to be stored. Out of plane constraints have no such symmetry and are matched exactly.

Parameters

a	Atom index of the first atom of the coordinate
b	Atom index of the second atom of the coordinate
c	Atom index of the third atom (for angles or torsions) or MaxIndex
d	Atom index of the fourth atom (for torsions) or MaxIndex

isValid()

bool isValid

(

Index

atomCount

)

const

Check that every atom this constraint names still exists.

Parameters

atomCount

The number of atoms available

Returns

True if the constraint can be evaluated against that many atoms

Constraints outlive the atoms they name, since deleting an atom leaves the stored indices behind.

evaluate()

bool evaluate	(	const Array< Vector3 > &	positions,
		Real &	value ) const

Measure this constraint's coordinate in a set of atomic positions, which need not be the molecule's active one – a trajectory or relaxed scan can be measured frame by frame.

Parameters

positions	The atomic positions to measure
value	Receives the measurement: Angstrom for a distance, degrees for an angle or torsion, matching value()

Returns

True if the constraint could be measured, false if it names an atom the positions do not have or has no single coordinate (out of plane)

setType()

void setType

(

Constraint::Type

type

)

const

Set the type of constraint. An explicit type survives later set() calls, since it cannot always be inferred from the atom indices – an out-of-plane constraint has the same four indices as a torsion. Pass None to go back to inferring the type from the indices.

Parameters

type	The type of constraint

Member Data Documentation

DefaultDistanceK

Real DefaultDistanceK = 41840.0

staticconstexpr

Default force constant for distance restraints, in kJ/mol/Angstrom^2

DefaultAngularK

Real DefaultAngularK = 10000.0

staticconstexpr

Default force constant for angular restraints, in kJ/mol/radian^2

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

• constraint.h