.. SPDX-FileCopyrightText: 2019-2020 Intel Corporation
..
.. SPDX-License-Identifier: CC-BY-4.0

.. _onemath_rng_lognormal:

lognormal
=========

Class is used for generation of lognormally distributed real types random numbers.

.. _onemath_rng_lognormal_description:

.. rubric:: Description

The class object is used in the :ref:`oneapi::math::rng::generate()<onemath_rng_generate>` function to provide random numbers lognormally distributed with mean :math:`(m, a)` and standard deviation :math:`(s, \sigma)` of subject normal distribution, displacement :math:`(displ, b)`, and scalefactor :math:`(scale, \beta)`, where :math:`a, \sigma, b, \beta \in R; \sigma > 0; \beta > 0`.

The probability distribution is given by:

.. math::

    f_{a, \sigma, b, \beta}(x) = \left\{ \begin{array}{rcl} \frac{1}{\sigma(x - b)\sqrt{2\pi}}exp(-\frac{[ln((x - b) / \beta) - a]^2}{2*\sigma^2}), x > b \\ 0, x \leq b \end{array}\right.

The cumulative distribution function is as follows:

.. math::

    F_{a, \sigma, b, \beta}(x) = \left\{ \begin{array}{rcl} \Phi( \frac{(ln((x - b) / \beta) - a)}{\sigma}), x > b \\ 0, x \leq b \end{array}\right.

.. _onemath_rng_lognormal_syntax:

class lognormal
---------------

.. rubric:: Syntax

.. code-block:: cpp

    namespace oneapi::math::rng {
    template<typename RealType = float, typename Method = lognormal_method::by_default>
    class lognormal {
    public:
        using method_type = Method;
        using result_type = RealType;
        lognormal();
        explicit lognormal(RealType m, RealType s, RealType displ = static_cast<RealType>(0.0), RealType scale = static_cast<RealType>(1.0));
        RealType m() const;
        RealType s() const;
        RealType displ() const;
        RealType scale() const;
    };
    }

.. container:: section

    .. rubric:: Template parameters

    .. container:: section

        typename RealType
            Type of the produced values. Supported types:
                * ``float``
                * ``double``

    .. container:: section

        typename Method = oneapi::math::rng::lognormal_method::by_default
            Transformation method, which will be used for generation. Supported types:

                * ``oneapi::math::rng::lognormal_method::by_default``
                * ``oneapi::math::rng::lognormal_method::box_muller2``
                * ``oneapi::math::rng::lognormal_method::icdf``
                * ``oneapi::math::rng::lognormal_method::box_muller2_accurate``
                * ``oneapi::math::rng::lognormal_method::icdf_accurate``

            See description of the methods in :ref:`Distributions methods template parameter<onemath_rng_distributions_template_parameter_onemath_rng_method_values>`.

.. container:: section

    .. rubric:: Class Members

    .. list-table::
        :header-rows: 1

        * - Routine
          - Description
        * - `lognormal()`_
          - Default constructor
        * - `explicit lognormal(RealType m, RealType s, RealType displ = static_cast<RealType>(0.0), RealType scale = static_cast<RealType>(1.0))`_
          - Constructor with parameters
        * - `RealType m() const`_
          - Method to obtain mean value
        * - `RealType s() const`_
          - Method to obtain standard deviation value
        * - `RealType displ() const`_
          - Method to obtain displacement value
        * - `RealType scale() const`_
          - Method to obtain scalefactor value

.. container:: section

    .. rubric:: Member types

    .. container:: section

        .. code-block:: cpp

            lognormal::method_type = Method

        .. container:: section

            .. rubric:: Description

            The type which defines transformation method for generation.

    .. container:: section

        .. code-block:: cpp

            lognormal::result_type = RealType

        .. container:: section

            .. rubric:: Description

            The type which defines type of generated random numbers.

.. container:: section

    .. rubric:: Constructors

    .. container:: section

        .. _`lognormal()`:

        .. code-block:: cpp

            lognormal::lognormal()

        .. container:: section

            .. rubric:: Description

            Default constructor for distribution, parameters set as `m` = 0.0, `s` = 1.0, `displ` = 0.0, `scale` = 1.0.

    .. container:: section

        .. _`explicit lognormal(RealType m, RealType s, RealType displ = static_cast<RealType>(0.0), RealType scale = static_cast<RealType>(1.0))`:

        .. code-block:: cpp

            explicit lognormal::lognormal(RealType m, RealType s, RealType displ = static_cast<RealType>(0.0), RealType scale = static_cast<RealType>(1.0))

        .. container:: section

            .. rubric:: Description

            Constructor with parameters. `m` is a mean value, `s` is a standard deviation value, `displ` is a displacement value, `scale` is a scalefactor value.

        .. container:: section

            .. rubric:: Throws

            oneapi::math::invalid_argument
                Exception is thrown when :math:`s \leq` static_cast<RealType>(0.0), or :math:`scale \leq` static_cast<RealType>(0.0)

.. container:: section

    .. rubric:: Characteristics

    .. container:: section

        .. _`RealType m() const`:

        .. code-block:: cpp

            RealType lognormal::m() const

        .. container:: section

            .. rubric:: Return Value

            Returns the distribution parameter `m` - mean value.

    .. container:: section

        .. _`RealType s() const`:

        .. code-block:: cpp

            RealType lognormal::s() const

        .. container:: section

            .. rubric:: Return Value

            Returns the distribution parameter `s` - standard deviation value.

    .. container:: section

        .. _`RealType displ() const`:

        .. code-block:: cpp

            RealType lognormal::displ() const

        .. container:: section

            .. rubric:: Return Value

            Returns the distribution parameter `displ` - displacement value.

    .. container:: section

        .. _`RealType scale() const`:

        .. code-block:: cpp

            RealType lognormal::scale() const

        .. container:: section

            .. rubric:: Return Value

            Returns the distribution parameter `scale` - scalefactor value.

**Parent topic:** :ref:`onemath_rng_distributions`