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%feature("docstring") OT::DiracCovarianceModel
"Dirac covariance function.

Available constructors:
    DiracCovarianceModel(*spatialDim, amplitude*)

    DiracCovarianceModel(*spatialDim, amplitude, spatialCorrelation*)

    DiracCovarianceModel(*spatialDim, spatialCovariance*)

Parameters
----------
spatialDim : int
    Dimension of the domain :math:`\\\\cD`.
amplitude : sequence of float
    Vector :math:`\\\\vect{\\\\sigma}` of dimension :math:`d`.
spatialCorrelation : :class:`~openturns.CorrelationMatrix`
    Correlation matrix :math:`\\\\mat{R} \\\\in \\\\mathcal{M}_{d \\\\times d}([-1, 1])`.
spatialCovariance : :class:`~openturns.CovarianceMatrix`
    Covariance matrix :math:`C^{stat} \\\\in \\\\mathcal{M}^{+}_{d \\\\times d}(\\\\Rset)`.

Notes
-----
The Dirac model defines a stationary covariance function
:math:`C^{stat}(\\\\vect{\\\\tau}) = C(\\\\vect{s}, \\\\vect{s}+\\\\vect{\\\\tau}) \\\\forall (\\\\vect{s},\\\\vect{\\\\tau}) \\\\in \\\\cD`
such that :

.. math::

    \\\\forall \\\\vect{\\\\tau} \\\\in \\\\cD,\\\\quad
    C^{stat}( \\\\vect{\\\\tau} )= 1_{\\\\tau=0} \\\\times \\\\left[\\\\vect{\\\\Sigma}\\\\right] \\\\,\\\\mat{R}\\\\, \\\\left[ \\\\mat{\\\\Sigma}\\\\right]

where :math:`\\\\mat{R} \\\\in  \\\\mathcal{M}_{d \\\\times d}([-1, 1])` is a correlation
matrix, :math:`\\\\mat{\\\\Sigma} \\\\in \\\\mathcal{M}_{d \\\\times d}(\\\\Rset)` is defined by:

.. math::

 \\\\mat{\\\\Sigma}= \\\\mbox{Diag}(\\\\sigma_1, \\\\dots, \\\\sigma_d)

with :math:`\\\\sigma_i>0` for any :math:`i`. :math:`\\\\vect{\\\\sigma}` is the amplitude vector.

The model is used for example in linear regression. Indeed, in that context, error is considered to be gaussian with `homoscedasticitc` variance
(same variance distribution, independent spatial correlation)

Examples
--------
Create two *DiracCovarianceModel* of dimension 2:

>>> import openturns as ot
>>> spatialDimension = 3
>>> amplitude = [1., 2.]
>>> correlation = ot.CorrelationMatrix(2)
>>> correlation[1,0] = 0.1
>>> covarianceModel = ot.DiracCovarianceModel(spatialDimension, amplitude)
>>> covarianceModelCorr = ot.DiracCovarianceModel(spatialDimension, amplitude, correlation)
"