 # class ROOT::Math::IntegratorOneDim

```

User Class for performing numerical integration of a function in one dimension.
It uses the plug-in manager to load advanced numerical integration algorithms from GSL, which reimplements the
algorithms used in the QUADPACK, a numerical integration package written in Fortran.

integration over infinite and semi-infinite ranges and singular integrals.

The integration type is selected using the Integration::type enumeration
in the class constructor.
The default type is adaptive integration with singularity
(ADAPTIVESINGULAR or QAGS in the QUADPACK convention) applying a Gauss-Kronrod 21-point integration rule.
In the case of ADAPTIVE type, the integration rule can also be specified via the
Integration::GKRule. The default rule is 31 points.

In the case of integration over infinite and semi-infinite ranges, the type used is always
ADAPTIVESINGULAR applying a transformation from the original interval into (0,1).

The ADAPTIVESINGULAR type is the most sophicticated type. When performances are
important, it is then recommened to use the NONADAPTIVE type in case of smooth functions or
ADAPTIVE with a lower Gauss-Kronrod rule.

For detailed description on GSL integration algorithms see the
<A HREF="http://www.gnu.org/software/gsl/manual/gsl-ref_16.html#SEC248">GSL Manual</A>.

@ingroup Integration

```

#### This class is also known as (typedefs to this class)

ROOT::Math::Integrator

## Function Members (Methods)

public:
 virtual ~IntegratorOneDim() double Error() const ROOT::Math::VirtualIntegratorOneDim* GetIntegrator() double Integral() double Integral(const ROOT::Math::IGenFunction& f) double Integral(const vector& pts) double Integral(const ROOT::Math::IGenFunction& f, const vector& pts) double Integral(double a, double b) double Integral(const ROOT::Math::IGenFunction& f, double a, double b) double IntegralCauchy(double a, double b, double c) double IntegralCauchy(const ROOT::Math::IGenFunction& f, double a, double b, double c) double IntegralLow(double b) double IntegralLow(const ROOT::Math::IGenFunction& f, double b) double IntegralUp(double a) double IntegralUp(const ROOT::Math::IGenFunction& f, double a) ROOT::Math::IntegratorOneDim IntegratorOneDim(ROOT::Math::IntegrationOneDim::Type type = IntegrationOneDim::kADAPTIVE, double absTol = 1.E-9, double relTol = 1E-6, unsigned int size = 1000, unsigned int rule = 3) ROOT::Math::IntegratorOneDim IntegratorOneDim(const ROOT::Math::IGenFunction& f, ROOT::Math::IntegrationOneDim::Type type = IntegrationOneDim::kADAPTIVE, double absTol = 1.E-9, double relTol = 1E-6, unsigned int size = 1000, int rule = 3) double operator()(double x) double Result() const void SetAbsTolerance(double absTolerance) void SetFunction(const ROOT::Math::IGenFunction& f, bool copy = false) void SetFunction(const ROOT::Math::IMultiGenFunction& f, unsigned int icoord = 0, const double* x = 0) void SetRelTolerance(double relTolerance) int Status() const
protected:
 ROOT::Math::VirtualIntegratorOneDim* CreateIntegrator(ROOT::Math::IntegrationOneDim::Type type, double absTol, double relTol, unsigned int size, int rule)
private:
 ROOT::Math::IntegratorOneDim IntegratorOneDim(const ROOT::Math::IntegratorOneDim&) ROOT::Math::IntegratorOneDim& operator=(const ROOT::Math::IntegratorOneDim&)

## Data Members

private:
 ROOT::Math::VirtualIntegratorOneDim* fIntegrator pointer to integrator interface class

## Class Charts ## Function documentation

void SetFunction(const Function & f)
double Integral(const ROOT::Math::IGenFunction& f, double a, double b)
double Integral(const Function & f)
double IntegralLow(const ROOT::Math::IGenFunction& f, double b)
double IntegralUp(const ROOT::Math::IGenFunction& f, double a)
double Integral(const Function & f, const std::vector<double> & pts)
double IntegralCauchy(const ROOT::Math::IGenFunction& f, double a, double b, double c)
IntegratorOneDim(ROOT::Math::IntegrationOneDim::Type type = IntegrationOneDim::kADAPTIVE, double absTol = 1.E-9, double relTol = 1E-6, unsigned int size = 1000, unsigned int rule = 3)
``` constructors

Constructor of one dimensional Integrator, default type is adaptive

@param absTol desired absolute Error
@param relTol desired relative Error
@param size maximum number of sub-intervals
@param rule  Gauss-Kronrod integration rule (only for GSL kADAPTIVE type)

Possible type values are : kGAUSS (simple Gauss method), kADAPTIVE (from GSL), kADAPTIVESINGULAR (from GSL), kNONADAPTIVE (from GSL)
Possible rule values are kGAUS15 (rule = 1), kGAUS21( rule = 2), kGAUS31(rule =3), kGAUS41 (rule=4), kGAUS51 (rule =5), kGAUS61(rule =6)
lower rules are indicated for singular functions while higher for smooth functions to get better accuracies

```
IntegratorOneDim(const ROOT::Math::IGenFunction& f, ROOT::Math::IntegrationOneDim::Type type = IntegrationOneDim::kADAPTIVE, double absTol = 1.E-9, double relTol = 1E-6, unsigned int size = 1000, int rule = 3)
```       Constructor of one dimensional Integrator passing a function interface

@param f      integration function (1D interface). It is copied inside
@param absTol desired absolute Error
@param relTol desired relative Error
@param size maximum number of sub-intervals
@param rule Gauss-Kronrod integration rule (only for GSL ADAPTIVE type)

```
SetFunction(const ROOT::Math::IGenFunction& f, bool copy = false)
IntegratorOneDim(const ROOT::Math::IGenFunction& f, ROOT::Math::IntegrationOneDim::Type type = IntegrationOneDim::kADAPTIVE, double absTol = 1.E-9, double relTol = 1E-6, unsigned int size = 1000, int rule = 3)
```        Template Constructor of one dimensional Integrator passing a generic function object

@param f      integration function (any C++ callable object implementing operator()(double x)
@param absTol desired absolute Error
@param relTol desired relative Error
@param size maximum number of sub-intervals
@param rule Gauss-Kronrod integration rule (only for GSL ADAPTIVE type)

```
virtual ~IntegratorOneDim()
``` destructor (will delete contained pointer)
```
IntegratorOneDim & operator=(const ROOT::Math::IntegratorOneDim& )
`{ return *this; }`
double Integral(const ROOT::Math::IGenFunction& f, double a, double b)
``` integration methods using a function

evaluate the Integral of a function f over the defined interval (a,b)
@param f integration function. The function type must be a C++ callable object implementing operator()(double x)
@param a lower value of the integration interval
@param b upper value of the integration interval

```
double Integral(const ROOT::Math::IGenFunction& f, double a, double b)
```       evaluate the Integral of a function f over the defined interval (a,b)
@param f integration function. The function type must implement the mathlib::IGenFunction interface
@param a lower value of the integration interval
@param b upper value of the integration interval

```
return Integral(a,b)
double IntegralUp(const ROOT::Math::IGenFunction& f, double a)
```      evaluate the Integral of a function f over the semi-infinite interval (a,+inf)
@param f integration function. The function type must be a C++ callable object implementing operator()(double x)
@param a lower value of the integration interval

```
double IntegralLow(const ROOT::Math::IGenFunction& f, double b)
```      evaluate the Integral of a function f over the over the semi-infinite interval (-inf,b)
@param f integration function. The function type must be a C++ callable object implementing operator()(double x)
@param b upper value of the integration interval

```
double IntegralCauchy(const ROOT::Math::IGenFunction& f, double a, double b, double c)
```      evaluate the Cauchy principal value of the integral of  a function f over the defined interval (a,b) with a singularity at c
@param f integration function. The function type must be a C++ callable object implementing operator()(double x)
@param a lower value of the integration interval
@param b upper value of the integration interval
@param c position of singularity

```
double operator()(double x)
```       define operator() for IntegralLow

```
double Result() const
```      return  the Result of the last Integral calculation

```
`{ return fIntegrator == 0 ? 0 : fIntegrator->Result(); }`
double Error() const
```      return the estimate of the absolute Error of the last Integral calculation

```
`{ return fIntegrator == 0 ? 0 : fIntegrator->Error(); }`
int Status() const
```      return the Error Status of the last Integral calculation

```
`{ return fIntegrator == 0 ? -1 : fIntegrator->Status(); }`
void SetRelTolerance(double relTolerance)
``` setter for control Parameters  (getters are not needed so far )

set the desired relative Error

```
`{ if (fIntegrator) fIntegrator->SetRelTolerance(relTolerance); }`
void SetAbsTolerance(double absTolerance)
```      set the desired absolute Error

```
`{ if (fIntegrator) fIntegrator->SetRelTolerance(absTolerance); }`
VirtualIntegratorOneDim * GetIntegrator()
```      return a pointer to integrator object

```
`{ return fIntegrator; }`
VirtualIntegratorOneDim * CreateIntegrator(ROOT::Math::IntegrationOneDim::Type type, double absTol, double relTol, unsigned int size, int rule)