ConditionedGaussianProcess¶

class ConditionedGaussianProcess(*args)

Conditioned Gaussian process.

ConditionedGaussianProcess(krigingResult, mesh)

Parameters
krigingResultKrigingResult

Structure that contains all elements of kriging computations.

meshMesh

Mesh over which the domain is discretized.

Notes

ConditionedGaussianProcess helps to create Gaussian random fields, where , with covariance function ( in the stationary case), conditionaly to some observations.

Let be the observations of the Gaussian process. We assume the same Gaussian prior as in the KrigingAlgorithm:

with a general linear model, a zero-mean Gaussian process with a stationary autocorrelation function :

The ConditionedGaussianProcess generates realizations of the conditioned process. It focuses first on the KrigingAlgorithm to build such prior. Results are stored in a KrigingResult structure, which is given as input argument of the class. This last one, combined with the mesh argument, define both the prior and the covariance evaluation on the mesh vertices conditionnaly to the previous observations. It follows that the realizations are randomly generated from the Gaussian distribution .

In practice, we do not store the Gaussian distribution as we need only the random realization method. For that purpose, we use the Cholesky method : we compute the Cholesky factor of the covariance matrix such as . It follows that the random realizations are obtained as following : with a centered & reduced random Gaussian realization.

Examples

>>> import openturns as ot
>>> ot.RandomGenerator.SetSeed(0)
>>> # Kriging use case
>>> # Learning data
>>> levels = [8.0, 5.0]
>>> box = ot.Box(levels)
>>> inputSample = box.generate()
>>> # Scale each direction
>>> inputSample *= 10
>>> # Define model
>>> model = ot.SymbolicFunction(['x', 'y'], ['cos(0.5*x) + sin(y)'])
>>> outputSample = model(inputSample)
>>> # Definition of exponential model
>>> inputDimension = 2
>>> covarianceModel = ot.SquaredExponential([1.988, 0.924], [3.153])
>>> # Basis definition
>>> basis = ot.ConstantBasisFactory(inputDimension).build()
>>> # Kriring algorithm
>>> algo = ot.KrigingAlgorithm(inputSample, outputSample, covarianceModel, basis)
>>> algo.run()
>>> result = algo.getResult()
>>> vertices = [[1.0, 0.0], [2.0, 0.0], [2.0, 1.0], [1.0, 1.0], [1.5, 0.5]]
>>> simplices = [[0, 1, 4], [1, 2, 4], [2, 3, 4], [3, 0, 4]]
>>> mesh2D = ot.Mesh(vertices, simplices)
>>> process = ot.ConditionedGaussianProcess(result, mesh2D)

Attributes
thisown

The membership flag

Methods

 Accessor to the object’s name. Get a continuous realization. Get the covariance model. Get the description of the process. getFuture(*args) Prediction of the future iterations of the process. Accessor to the object’s id. Get the dimension of the domain . getMarginal(indices) Get the marginal of the random process. Get the mesh. Accessor to the object’s name. Get the dimension of the domain . Return a realization of the process. getSample(size) Get realizations of the process. Accessor to the object’s shadowed id. Get the time grid of observation of the process. Get the trend function. Accessor to the object’s visibility state. Test if the object is named. Test if the object has a distinguishable name. Test whether the process is composite or not. Test whether the process is normal or not. Test whether the process is stationary or not. Tell if the process is trend stationary or not. setDescription(description) Set the description of the process. setMesh(*args) Set the mesh. setName(name) Accessor to the object’s name. setSamplingMethod(*args) Set the used method for getRealization. Accessor to the object’s shadowed id. setTimeGrid(*args) Set the time grid of observation of the process. setVisibility(visible) Accessor to the object’s visibility state.
__init__(*args)

Initialize self. See help(type(self)) for accurate signature.

getClassName()

Accessor to the object’s name.

Returns
class_namestr

The object class name (object.__class__.__name__).

getContinuousRealization()

Get a continuous realization.

Returns
realizationFunction

According to the process, the continuous realizations are built:

• either using a dedicated functional model if it exists: e.g. a functional basis process.

• or using an interpolation from a discrete realization of the process on : in dimension , a linear interpolation and in dimension , a piecewise constant function (the value at a given position is equal to the value at the nearest vertex of the mesh of the process).

getCovarianceModel()

Get the covariance model.

Returns
covarianceModelCovarianceModel

Temporal covariance model .

getDescription()

Get the description of the process.

Returns
descriptionDescription

Description of the process.

getFuture(*args)

Prediction of the future iterations of the process.

Parameters
stepNumberint,

Number of future steps.

sizeint, , optional

Number of futures needed. Default is 1.

Returns
prediction

future iterations of the process. If , prediction is a TimeSeries. Otherwise, it is a ProcessSample.

getId()

Accessor to the object’s id.

Returns
idint

Internal unique identifier.

getInputDimension()

Get the dimension of the domain .

Returns
nint

Dimension of the domain : .

getMarginal(indices)

Get the marginal of the random process.

Parameters
kint or list of ints

Index of the marginal(s) needed.

Returns
marginalsProcess

Process defined with marginal(s) of the random process.

getMesh()

Get the mesh.

Returns
meshMesh

Mesh over which the domain is discretized.

getName()

Accessor to the object’s name.

Returns
namestr

The name of the object.

getOutputDimension()

Get the dimension of the domain .

Returns
dint

Dimension of the domain .

getRealization()

Return a realization of the process.

Returns
realizationField

A realization of the process.

Examples

>>> import openturns as ot
>>> ot.RandomGenerator.SetSeed(0)
>>> # Kriging use case
>>> # Learning data
>>> levels = [8.0, 5.0]
>>> box = ot.Box(levels)
>>> inputSample = box.generate()
>>> # Scale each direction
>>> inputSample *= 10
>>> # Define model
>>> model = ot.SymbolicFunction(['x', 'y'], ['cos(0.5*x) + sin(y)'])
>>> outputSample = model(inputSample)
>>> # Definition of exponential model
>>> inputDimension = 2
>>> covarianceModel = ot.SquaredExponential(inputDimension *[0.95])
>>> # Basis definition
>>> basis = ot.ConstantBasisFactory(inputDimension).build()
>>> # Kriring algorithm
>>> algo = ot.KrigingAlgorithm(inputSample, outputSample, covarianceModel, basis)
>>> algo.run()
>>> result = algo.getResult()
>>> vertices = [[1.0, 0.0], [2.0, 0.0], [2.0, 1.0],[1.0, 1.0], [1.5, 0.5]]
>>> simplices = [[0, 1, 4], [1, 2, 4], [2, 3, 4], [3, 0, 4]]
>>> mesh2D = ot.Mesh(vertices, simplices)
>>> process = ot.ConditionedGaussianProcess(result, mesh2D)
>>> # Get a realization of the process
>>> realization = process.getRealization()

getSample(size)

Get realizations of the process.

Parameters
nint,

Number of realizations of the process needed.

Returns
processSampleProcessSample

realizations of the random process. A process sample is a collection of fields which share the same mesh .

getShadowedId()

Accessor to the object’s shadowed id.

Returns
idint

Internal unique identifier.

getTimeGrid()

Get the time grid of observation of the process.

Returns
timeGridRegularGrid

Time grid of a process when the mesh associated to the process can be interpreted as a RegularGrid. We check if the vertices of the mesh are scalar and are regularly spaced in but we don’t check if the connectivity of the mesh is conform to the one of a regular grid (without any hole and composed of ordered instants).

getTrend()

Get the trend function.

Returns
trendTrendTransform

Trend function.

getVisibility()

Accessor to the object’s visibility state.

Returns
visiblebool

Visibility flag.

hasName()

Test if the object is named.

Returns
hasNamebool

True if the name is not empty.

hasVisibleName()

Test if the object has a distinguishable name.

Returns
hasVisibleNamebool

True if the name is not empty and not the default one.

isComposite()

Test whether the process is composite or not.

Returns
isCompositebool

True if the process is composite (built upon a function and a process).

isNormal()

Test whether the process is normal or not.

Returns
isNormalbool

True if the process is normal.

Notes

A stochastic process is normal if all its finite dimensional joint distributions are normal, which means that for all and , with , there is and such that:

where , and and is the symmetric matrix:

A Gaussian process is entirely defined by its mean function and its covariance function (or correlation function ).

isStationary()

Test whether the process is stationary or not.

Returns
isStationarybool

True if the process is stationary.

Notes

A process is stationary if its distribution is invariant by translation: , , , we have:

isTrendStationary()

Tell if the process is trend stationary or not.

Returns
isTrendStationarybool

True if the process is trend stationary.

setDescription(description)

Set the description of the process.

Parameters
descriptionsequence of str

Description of the process.

setMesh(*args)

Set the mesh.

Parameters
meshMesh

Mesh over which the domain is discretized.

setName(name)

Accessor to the object’s name.

Parameters
namestr

The name of the object.

setSamplingMethod(*args)

Set the used method for getRealization.

Available parameters are :

• 0 : Cholesky factor sampling (default method)

• 1 : H-Matrix method (if H-Mat available)

• 2 : Gibbs method (in dimension 1 only)

Parameters
samplingMethodint

Fix a method for sampling.

setShadowedId(id)

Accessor to the object’s shadowed id.

Parameters
idint

Internal unique identifier.

setTimeGrid(*args)

Set the time grid of observation of the process.

Returns
timeGridRegularGrid

Time grid of observation of the process when the mesh associated to the process can be interpreted as a RegularGrid. We check if the vertices of the mesh are scalar and are regularly spaced in but we don’t check if the connectivity of the mesh is conform to the one of a regular grid (without any hole and composed of ordered instants).

setVisibility(visible)

Accessor to the object’s visibility state.

Parameters
visiblebool

Visibility flag.

thisown

The membership flag