# sc_Function - Man Page

The Function class is an abstract base class that, given a set of coordinates, will compute a value and possibly a gradient and hessian at that point.

## Synopsis

`#include <function.h>`

Inherits **sc::SavableState**, and **sc::Compute**.

Inherited by **sc::MolecularEnergy**, and **sc::Volume**.

### Public Member Functions

**Gradient Members**

These are analogous to the routines that deal with values, but work with gradients instead.

virtual **RefSCVector gradient** ()

int **gradient_needed** () const

int **do_gradient** (int)

virtual void **set_desired_gradient_accuracy** (double)

virtual double **actual_gradient_accuracy** () const

virtual double **desired_gradient_accuracy** () const**AccResultRefSCVector** & **gradient_result** ()

**Hessian Members**

These are analogous to the routines that deal with values, but work with the hessian instead.

virtual **RefSymmSCMatrix hessian** ()

int **hessian_needed** () const

int **do_hessian** (int)

virtual void **set_desired_hessian_accuracy** (double)

virtual double **actual_hessian_accuracy** () const

virtual double **desired_hessian_accuracy** () const**AccResultRefSymmSCMatrix** & **hessian_result** ()

virtual void **guess_hessian** (**RefSymmSCMatrix** &)**Compute** a quick, approximate hessian.

virtual **RefSymmSCMatrix inverse_hessian** (**RefSymmSCMatrix** &)

virtual int **value_implemented** () const

Information about the availability of values, gradients, and hessians.

virtual int **gradient_implemented** () const

virtual int **hessian_implemented** () const

virtual void **set_x** (const **RefSCVector** &)

Set and retrieve the coordinate values. **RefSCVector get_x** () const

const **RefSCVector** & **get_x_no_copy** () const

virtual **Ref**< **NonlinearTransform** > **change_coordinates** ()

An optimizer can call change coordinates periodically to give the function an opportunity to change its coordinate system.

virtual void **print** (std::ostream &=**ExEnv::out0**()) const

Print information about the object.

### Protected Member Functions

**Update Members**

Update the various computable results.

virtual void **set_value** (double)

virtual void **set_gradient** (**RefSCVector** &)

virtual void **set_hessian** (**RefSymmSCMatrix** &)

virtual void **set_matrixkit** (const **Ref**< **SCMatrixKit** > &)

Set the **SCMatrixKit** that should be used to construct the requisite vectors and matrices.

virtual void **set_dimension** (const **RefSCDimension** &)

### Protected Attributes

**Ref**< **SCMatrixKit** > **matrixkit_**

Used to construct new matrices. **RefSCVector x_**

The variables. **RefSCDimension dim_**

The dimension of x_. **AccResultdouble value_**

The value of the function at x_. **AccResultRefSCVector gradient_**

The gradient at x_. **AccResultRefSymmSCMatrix hessian_**

The hessian at x_.

### Accuracy Setting Members

Set the accuracies with which the various computables have been computed.

virtual void **set_actual_value_accuracy** (double)

virtual void **set_actual_gradient_accuracy** (double)

virtual void **set_actual_hessian_accuracy** (double)**RefSCVector** & **get_x_reference** ()

Get read/write access to the coordinates for modification.

void **do_change_coordinates** (const **Ref**< **NonlinearTransform** > &)

Change the coordinate system and apply the given transform to intermediates matrices and vectors. **Function** ()**Function** (**StateIn** &)**Function** (const **Function** &)**Function** (const **Ref**< **KeyVal** > &, double funcacc=DBL_EPSILON, double gradacc=DBL_EPSILON, double hessacc=DBL_EPSILON)

The keyval constructor reads the following keywords:

virtual **~Function** ()**Function** & **operator=** (const **Function** &)**Ref**< **SCMatrixKit** > **matrixkit** () const

Return the **SCMatrixKit** used to construct vectors and matrices. **RefSCDimension dimension** () const

Return the **SCDimension** of the problem.

virtual 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.

virtual double **value** ()

Return the value of the function.

int **value_needed** () const

Returns nonzero if the current value is not up-to-date.

int **do_value** (int)

If passed a nonzero number, compute the value the next time **compute()** is called. **AccResultdouble** & **value_result** ()

virtual void **set_desired_value_accuracy** (double)

Set the accuracy to which the value is to be computed.

virtual double **actual_value_accuracy** () const

Return the accuracy with which the value has been computed.

virtual double **desired_value_accuracy** () const

Return the accuracy with which the value is to be computed.

### Additional Inherited Members

## Detailed Description

The **Function** class is an abstract base class that, given a set of coordinates, will compute a value and possibly a gradient and hessian at that point.

## Constructor & Destructor Documentation

### sc::Function::Function (const Ref< KeyVal > &, double funcacc = DBL_EPSILON, double gradacc = DBL_EPSILON, double hessacc = DBL_EPSILON)

The keyval constructor reads the following keywords:

- matrixkit
Gives a

**SCMatrixKit**object. If it is not specified, a default**SCMatrixKit**is selected.- value_accuracy
Sets the accuracy to which values are computed. The default is the machine accuracy.

- gradient_accuracy
Sets the accuracy to which gradients are computed. The default is the machine accuracy.

- hessian_accuracy
Sets the accuracy to which hessians are computed. The default is the machine accuracy.

## Member Function Documentation

### virtual Ref<NonlinearTransform> sc::Function::change_coordinates () [virtual]

An optimizer can call change coordinates periodically to give the function an opportunity to change its coordinate system. A return value of 0 means the coordinates were not changed. Otherwise, a transform object to the new coordinate system is return. The function object applies the transform to any objects it contains. This will obsolete the function data.

Reimplemented in **sc::MolecularEnergy**.

### int sc::Function::do_value (int)

If passed a nonzero number, compute the value the next time **compute()** is called. Return a nonzero number if the value was previously to be computed.

### virtual void sc::Function::save_data_state (StateOut &) [virtual]

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::SavableState**.

Reimplemented in **sc::Wavefunction**, **sc::HCoreWfn**, **sc::OneBodyWavefunction**, **sc::ExtendedHuckelWfn**, **sc::UnrestrictedSCF**, **sc::UHF**, **sc::TCSCF**, **sc::TCHF**, **sc::SCF**, **sc::OSSSCF**, **sc::OSSHF**, **sc::HSOSSCF**, **sc::HSOSHF**, **sc::CLSCF**, **sc::CLHF**, **sc::PsiCCSD_T**, **sc::PsiCCSD**, **sc::PsiSCF**, **sc::PsiWavefunction**, **sc::MBPT2_R12**, **sc::MP2BasisExtrap**, **sc::MBPT2**, **sc::UKS**, **sc::HSOSKS**, **sc::CLKS**, **sc::TaylorMolecularEnergy**, **sc::SumMolecularEnergy**, and **sc::MolecularEnergy**.

## Author

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