Example user function implementing a third-order polynomial. More...

#include <PUserFcn.h>

Inheritance diagram for PUserFcn:

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Collaboration diagram for PUserFcn:

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Public Member Functions
	PUserFcn ()
	Default constructor.

	~PUserFcn ()
	Destructor.

Double_t	operator() (Double_t t, const std::vector< Double_t > &param) const
	Evaluates the third-order polynomial at time t.

Public Member Functions inherited from PUserFcnBase
	PUserFcnBase ()
	Default constructor.

virtual	~PUserFcnBase ()
	Virtual destructor.

virtual Bool_t	NeedGlobalPart () const

virtual void	SetGlobalPart (std::vector< void * > &globalPart, UInt_t idx)

virtual Bool_t	GlobalPartIsValid () const

Detailed Description

Example user function implementing a third-order polynomial.

PUserFcn demonstrates how to create custom theory functions by deriving from PUserFcnBase. This example implements a cubic polynomial:

$P(t) = a_0 + a_1 t + a_2 t^2 + a_3 t^3$

where $a_0, a_1, a_2, a_3$ are the polynomial coefficients passed as fit parameters.

Usage in MSR File

To use this function in your analysis:

FITPARAMETER
#  No Name       Value  Step   Pos_Error Boundaries
    1 a0         1.0    0.1    none
    2 a1         0.01   0.001  none
    3 a2         0.001  0.0001 none
    4 a3         0.0001 0.00001 none
 
THEORY
userFcn  libPUserFcn.so  PUserFcn  1 2 3 4  (a0, a1, a2, a3)

Applications

Polynomial backgrounds are useful for:

Modeling baseline drifts in long-time measurements
Phenomenological fits to slowly varying relaxation
Testing the user function infrastructure

As a Template

This class serves as a minimal working example for creating custom user functions. To create your own:

Copy PUserFcn.h and PUserFcn.cpp
Rename the class and update the ClassDef/ClassImp macros
Implement your physics in the operator() method
Create a LinkDef.h and build as a shared library

See also: PUserFcnBase for the abstract interface and detailed implementation guide; PTheory for how user functions are loaded and evaluated

Definition at line 85 of file PUserFcn.h.

Constructor & Destructor Documentation

◆ PUserFcn()

PUserFcn::PUserFcn ( )

Default constructor.

References PUserFcn().

Referenced by PUserFcn().

◆ ~PUserFcn()

PUserFcn::~PUserFcn ( )

Destructor.

Destructor for PUserFcn.

Cleans up any resources allocated by the polynomial function. Since this implementation has no dynamically allocated resources, the destructor is empty.

Note: User functions with allocated resources (lookup tables, buffers, external library handles) must clean them up here to prevent memory leaks. If using the global part interface, ensure proper coordination with gGlobalUserFcn cleanup.

Definition at line 65 of file PUserFcn.cpp.

Member Function Documentation

◆ operator()()

Double_t PUserFcn::operator()	(	Double_t	t,
		const std::vector< Double_t > &	param ) const

virtual

Evaluates the third-order polynomial at time t.

Evaluates the third-order polynomial at the given time.

Computes:

$P(t) = \texttt{param[0]} + \texttt{param[1]} \cdot t + \texttt{param[2]} \cdot t^2 + \texttt{param[3]} \cdot t^3$

Parameters

t	Time value (typically in microseconds)
param	Vector of polynomial coefficients: param[0]: constant term param[1]: linear coefficient (per μs) param[2]: quadratic coefficient (per μs²) param[3]: cubic coefficient (per μs³)

Returns: The polynomial value at time t

Computes a cubic polynomial of the form:

$P(t) = c_0 + c_1 t + c_2 t^2 + c_3 t^3 = \sum_{k=0}^{3} c_k t^k$

where the coefficients $c_k$ are provided in the parameter vector.

Example MSR Configuration

FITPARAMETER
#  No Name       Value     Step      Pos_Error Boundaries
    1 c0         0.95      0.01      none
    2 c1         -0.001    0.0001    none
    3 c2         0.00001   0.000001  none
    4 c3         0.0       0.0000001 none      0  none   (fixed to zero for quadratic)
 
THEORY
userFcn  libPUserFcn.so  PUserFcn  1 2 3 4

Implementation Notes

Uses direct polynomial evaluation (Horner's method could improve numerical stability for high-precision applications)
Asserts exactly 4 parameters to catch MSR file configuration errors
No special handling for negative time values

Parameters

t	Independent variable (time in μs for μSR, or general x-axis value for non-μSR fits)
param	Vector containing exactly 4 polynomial coefficients: param[0]: - constant term (dimensionless) param[1]: - linear coefficient (μs⁻¹) param[2]: - quadratic coefficient (μs⁻²) param[3]: - cubic coefficient (μs⁻³)