exponential.H

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    Copyright (C) 2011-2016 OpenFOAM Foundation
    Copyright (C) 2021 OpenCFD Ltd.
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License
    This file is part of OpenFOAM.
 
    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
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    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.
 
    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
Class
    Foam::distributionModels::exponential
 
Description
    Particle-size distribution model wherein random samples are drawn
    from the doubly-truncated exponential probability density function:
 
    \f[
        f(x; \lambda, A, B) =
            \lambda \frac{\exp(-\lambda (x - A))}{1 - \exp(-\lambda(B-A))}
    \f]
    where
 
    \vartable
        f(x; \lambda, A, B) | Exponential probability density function
        \lambda   | Rate parameter
        x         | Sample
        A         | Minimum of the distribution
        B         | Maximum of the distribution
    \endvartable
 
    Constraints:
    - \f$ \infty > B > A > 0 \f$
    - \f$ x \in [B,A] \f$
    - \f$ \lambda > 0 \f$
 
    Random samples are generated by the inverse transform sampling technique
    by using the quantile function of the doubly-truncated exponential
    probability density function:
 
    \f[
        x = - \frac{1}{\lambda} \ln (r)
    \f]
 
    with
 
    \f[
        r = q_{min} + u (q_{max} - q_{min})
    \f]
 
    \f[
        q_{min} = \exp(-\lambda A)
    \f]
 
    \f[
        q_{max} = \exp(-\lambda B)
    \f]
    where \f$ u \f$ is a sample drawn from the uniform probability
    density function on the unit interval \f$ (0, 1) \f$.
 
Usage
    Minimal example by using \c constant/<CloudProperties>:
    \verbatim
    subModels
    {
        injectionModels
        {
            <name>
            {
                ...
 
                sizeDistribution
                {
                    type        exponential;
                    exponentialDistribution
                    {
                        lambda      <lambdaValue>;
                        minValue    <minValue>;
                        maxValue    <maxValue>;
                    }
                }
            }
        }
    }
    \endverbatim
 
    where the entries mean:
    \table
      Property     | Description                       | Type | Reqd | Deflt
      type         | Type name: exponential            | word | yes  | -
      exponentialDistribution | Distribution settings  | dict | yes  | -
      lambda       | Rate parameter                    | scalar | yes  | -
      minValue     | Minimum of the distribution       | scalar | yes  | -
      maxValue     | Maximum of the distribution       | scalar | yes  | -
    \endtable
 
SourceFiles
    exponential.C
 
\*---------------------------------------------------------------------------*/
 
#ifndef distributionModels_exponential_H
#define distributionModels_exponential_H
 
#include "distributionModel.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
namespace distributionModels
{
 
/*---------------------------------------------------------------------------*\
                        Class exponential Declaration
\*---------------------------------------------------------------------------*/
 
class exponential
:
    public distributionModel
{
    // Private Data
 
        //- Rate parameter
        scalar lambda_;
 
 
public:
 
    //- Runtime type information
    TypeName("exponential");
 
 
    // Constructors
 
        //- Construct from components
        exponential(const dictionary& dict, Random& rndGen);
 
        //- Copy construct
        exponential(const exponential& p);
 
        //- Construct and return a clone
        virtual autoPtr<distributionModel> clone() const
        {
            return autoPtr<distributionModel>(new exponential(*this));
        }
 
        //- No copy assignment
        void operator=(const exponential&) = delete;
 
 
    //- Destructor
    virtual ~exponential() = default;
 
 
    // Member Functions
 
        //- Sample the distribution
        virtual scalar sample() const;
 
        //- Return the theoretical mean of the distribution
        virtual scalar meanValue() const;
};
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
} // End namespace distributionModels
} // End namespace Foam
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
#endif
 
// ************************************************************************* //