`#include <simple.h>`

Inherits **sc::IntCoor**.

Inherited by **sc::BendSimpleCo**, **sc::LinIPSimpleCo**, **sc::LinOPSimpleCo**, **sc::OutSimpleCo**, **sc::ScaledTorsSimpleCo**, **sc::StreSimpleCo**, and **sc::TorsSimpleCo**.

**SimpleCo** (int, const char *=0)

*This constructor takes an integer argument which is the number of atoms needed to describe the coordinate. *
**SimpleCo** (const **Ref**< **KeyVal** > &, int natom)

*The ***KeyVal** constructor requires the number of atoms.
int **natoms** () const

*Returns the number of atoms in the coordinate. *
int **operator[]** (int i) const

*Returns the index of the i’th atom in the coordinate. *
void **save_data_state** (**StateOut** &)

*Save the base classes (with save_data_state) and the members in the same order that the ***StateIn** CTOR initializes them.
**SimpleCo** (**StateIn** &)

virtual int **operator==** (**SimpleCo** &)

int **operator!=** (**SimpleCo** &u)

double **force_constant** (**Ref**< **Molecule** > &)

*Returns an approximate force constant (a la Almlof). *
void **update_value** (const **Ref**< **Molecule** > &)

*Recalculates the value of the coordinate based on the geometry in the ***Molecule**.
void **bmat** (const **Ref**< **Molecule** > &, **RefSCVector** &bmat, double coef=1.0)

*Fill in a row of the B matrix. *
virtual double **calc_force_con** (**Molecule** &)=0

*Calculates an approximate force constant and returns it’s value. *
virtual double **calc_intco** (**Molecule** &, double *=0, double=1)=0

*Calculate the value of the coordinate based on what’s in ***Molecule**.
void **print_details** (const **Ref**< **Molecule** > &, std::ostream &=**ExEnv::out0**()) const

*Print the coordinate. *
int **equivalent** (**Ref**< **IntCoor** > &)

*Tests to see if two coordinates are equivalent to each other. *

The **SimpleCo** abstract class describes a simple internal coordinate of a molecule.

The number atoms involved can be 2, 3 or 4 and is determined by the specialization of **SimpleCo**.

There are three ways to specify the atoms involved in the internal coordinate. The first way is a shorthand notation, just a vector of a label followed by the atom numbers (starting at 1) is given. For example, a stretch between two atoms, 1 and 2, is given, in the **ParsedKeyVal** format, as

stretch<StreSimpleCo>: [ R12 1 2 ]

The other two ways to specify the atoms are more general. With them, it is possible to give parameters for the **IntCoor** base class (and thus give the value of the coordinate). In the first of these input formats, a vector associated with the keyword atoms gives the atom numbers. The following specification for stretch is equivalent to that above:

stretch<StreSimpleCo>:( label = R12 atoms = [ 1 2 ] )

In the second, a vector, atom_labels, is given along with a **Molecule** object. The atom labels are looked up in the **Molecule** object to find the atom numbers. The following specification for stretch is equivalent to those above:

molecule<Molecule>: (
{ atom_labels atoms geometry } = {
H1 H [ 1.0 0.0 0.0 ]
H2 H [-1.0 0.0 0.0 ] } )
stretch<StreSimpleCo>:( label = R12
atom_labels = [ H1 H2 ]
molecule = $:molecule )

Calculate the value of the coordinate based on what’s in **Molecule**. If given a double*, fill in that part of the B matrix. If the bmatrix is to be calculated, the third argument gives the coefficient.

Tests to see if two coordinates are equivalent to each other. This is false if the atoms don’t match.

Implements **sc::IntCoor**.

Save the base classes (with save_data_state) and the members in the same order that the **StateIn** CTOR initializes them. This must be implemented by the derived class if the class has data.

Reimplemented from **sc::IntCoor**.

Recalculates the value of the coordinate based on the geometry in the **Molecule**.

Implements **sc::IntCoor**.