FunctionalChaosResult¶

class FunctionalChaosResult(*args)¶

Functional chaos result.

Returned by functional chaos algorithms, see FunctionalChaosAlgorithm.

Parameters:

sampleX2-d sequence of float: Input sample of $\inputRV \in \Rset^{\inputDim}$ .
sampleY2-d sequence of float: Output sample of $\outputRV \in \Rset^{\outputDim}$ .
distributionDistribution: Distribution of the random vector $\inputRV$
transformationFunction: The function that maps the physical input $\inputRV$ to the standardized input $\standardRV$ .
inverseTransformationFunction: The function that maps the standardized input $\standardRV$ to the physical input $\inputRV$ .
orthogonalBasisOrthogonalBasis: The multivariate orthogonal basis.
indicessequence of int: The indices of the selected basis function within the orthogonal basis.
alpha_k2-d sequence of float: The coefficients of the functional chaos expansion.
Psi_ksequence of Function: The functions of the multivariate basis selected by the algorithm.
isLeastSquaresbool: True if the expansion is computed using least squares.
isModelSelectionbool: True if the expansion is computed using model selection.

Methods

`drawErrorHistory`()	Draw the error history.
`drawSelectionHistory`()	Draw the basis selection history.
`getClassName`()	Accessor to the object's name.
`getCoefficients`()	Get the coefficients.
`getCoefficientsHistory`()	The coefficients values selection history accessor.
`getComposedMetaModel`()	Get the composed metamodel.
`getConditionalExpectation`(conditioningIndices)	Get the conditional expectation of the expansion given one vector input.
`getDistribution`()	Get the input distribution.
`getErrorHistory`()	The error history accessor.
`getIndices`()	Get the indices of the final basis.
`getIndicesHistory`()	The basis indices selection history accessor.
`getInputSample`()	Accessor to the input sample.
`getInverseTransformation`()	Get the inverse isoprobabilistic transformation.
`getMetaModel`()	Accessor to the metamodel.
`getName`()	Accessor to the object's name.
`getOrthogonalBasis`()	Get the orthogonal basis.
`getOutputSample`()	Accessor to the output sample.
`getReducedBasis`()	Get the reduced basis.
`getSampleResiduals`()	Get residuals sample.
`getTransformation`()	Get the isoprobabilistic transformation.
`hasName`()	Test if the object is named.
`involvesModelSelection`()	Get the model selection flag.
`isLeastSquares`()	Get the least squares flag.
`setErrorHistory`(errorHistory)	The error history accessor.
`setInputSample`(sampleX)	Accessor to the input sample.
`setInvolvesModelSelection`(involvesModelSelection)	Set the model selection flag.
`setIsLeastSquares`(isLeastSquares)	Set the least squares flag.
`setMetaModel`(metaModel)	Accessor to the metamodel.
`setName`(name)	Accessor to the object's name.
`setOutputSample`(sampleY)	Accessor to the output sample.
`setSelectionHistory`(indicesHistory, ...)	The basis coefficients and indices accessor.

getRelativeErrors
getResiduals
setRelativeErrors
setResiduals

Notes

Let $\sampleSize \in \Nset$ be the sample size. Let $\outputDim \in \Nset$ be the dimension of the output of the physical model. For any $j = 1, ..., \sampleSize$ and any $i = 1, ..., \outputDim$ , let $y_{j, i} \in \Rset$ be the output of the physical model and let $\hat{y}_{j, i} \in \Rset$ be the output of the metamodel. For any $i = 1, ..., \outputDim$ , let $\outputRV_i \in \Rset^\sampleSize$ be the sample output and let $\widehat{\outputRV}_i \in \Rset^\sampleSize$ be the output predicted by the metamodel. The marginal residual is:

$\hat{r}_i = \frac{\sqrt{SS_i}}{\sampleSize}$

for $i = 1, ..., \outputDim$ , where $SS_i$ is the marginal sum of squares:

$SS_i = \sum_{j = 1}^\sampleSize (y_{j, i} - \hat{y}_{j, i})^2.$

The marginal relative error is:

$\widehat{re}_i = \frac{\hat{r}_i / \sampleSize}{\hat{s}_{Y, i}^2}$

for $i = 1, ..., \outputDim$ , where $\hat{s}_{Y, i}^2$ is the unbiased sample variance of the $i$ -th output.

This structure is created by the method run() of FunctionalChaosAlgorithm, and obtained thanks to the getResult() method.

__init__(*args)¶

drawErrorHistory()¶

Draw the error history.

This is only available with LARS, and when the output dimension is 1.

Returns:

graphGraph: The evolution of the error at each selection iteration

drawSelectionHistory()¶

Draw the basis selection history.

This is only available with LARS, and when the output dimension is 1.

Returns:

graphGraph: The evolution of the basis coefficients at each selection iteration

getClassName()¶

Accessor to the object’s name.

Returns:

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

getCoefficients()¶

Get the coefficients.

Returns:

coefficients2-d sequence of float: Coefficients $(\vect{a_k})_{k \in \set{J}^P_s}$ .

getCoefficientsHistory()¶

The coefficients values selection history accessor.

This is only available with LARS, and when the output dimension is 1.

Returns:

coefficientsHistory2-d sequence of float: The coefficients values selection history, for each iteration. Each inner list gives the coefficients values of the basis terms at i-th iteration.

getComposedMetaModel()¶

Get the composed metamodel.

The composed metamodel is defined on the standard space $\standardInputSpace$ . It is defined by the equation:

$\tilde{h}(\standardReal) = \sum_{k \in \set{J}^P_s} \vect{a}_k \psi_k(\standardReal)$

for any $\standardReal \in \standardInputSpace$ .

Returns:

composedMetamodelFunction: The metamodel in the standard space $\standardInputSpace$ .

getConditionalExpectation(conditioningIndices)¶

Get the conditional expectation of the expansion given one vector input.

This method returns the functional chaos result corresponding to the conditional expectation of the output given an input vector. Indeed, the conditional expectation of a polynomial chaos expansion is, again, a polynomial chaos expansion. This is possible only if the marginals of the input distribution are independent. Otherwise, an exception is generated. An example is provided in Conditional expectation of a polynomial chaos expansion.

We consider the notations introduced in Functional Chaos Expansion. Let $\inputRV \in \Rset^{\inputDim}$ be the input and let $\vect{u} \subseteq \{1, ..., \inputDim\}$ be a set of marginal indices. Let $\inputRV_{\vect{u}} \in \Rset^{|\vect{u}|}$ be the vector corresponding to the group of input variables where $|\vect{u}| = \operatorname{card}(\vect{u})$ is the number of input variables in the group. Let $\metaModel(\inputRV)$ be the polynomial chaos expansion of the physical model $\model$ . This function returns the functional chaos expansion of:

$\metaModel_{\vect{u}}\left(\inputReal_{\vect{u}}\right) = \Expect{\metaModel(\inputRV) | \inputRV_{\vect{u}} = \inputReal_{\vect{u}}}$

for any $\inputReal_{\vect{u}} \in \Rset^{|\vect{u}|}$ .

Mathematical analysis

The mathematical derivation is better described in the standard space $\standardInputSpace$ than in the physical space $\physicalInputSpace$ and this is why we consider the former. Assume that the basis functions $\{\psi_{\vect{\alpha}}\}_{\vect{\alpha} \in \set{J}^P}$ are defined by the tensor product:

$\psi_{\vect{\alpha}}(\standardReal) = \prod_{i = 1}^\inputDim \pi_{\alpha_i}^{(i)}(z_i)$

for any $\vect{\alpha} \in \set{J}^P$ and any $\standardReal \in \standardInputSpace$ where $\left\{\pi_k^{(i)}\right\}_{k \geq 0}$ is the set of orthonormal polynomials of degree $k$ for the $i$ -th input marginal. Assume that the PCE to order $P$ is:

$\widetilde{h}(\standardReal) = \sum_{\vect{\alpha} \in \set{J}^P} a_{\vect{\alpha}} \psi_{\vect{\alpha}}(\standardReal)$

for any $\standardReal \in \standardInputSpace$ . Assume that the input marginals $\{Z_i\}_{i = 1, ..., \inputDim}$ are independent. Let $\vect{u} \subseteq \{1, ..., \inputDim\}$ be a group of variables with dimension $\operatorname{card}(\vect{u}) \in \Nset$ . Assume that $\standardInputSpace$ is the Cartesian product of vectors which have components in the group $\vect{u}$ and other components, i.e. assume that:

$\standardInputSpace = \standardInputSpace_{\vect{u}} \times \standardInputSpace_{\overline{\vect{u}}}$

where $\standardInputSpace_{\vect{u}} \subseteq \Rset^{|\vect{u}|}$ and $\standardInputSpace_{\overline{\vect{u}}} \subseteq \Rset^{|\overline{\vect{u}}|}$ . Let $\widetilde{h}_{\vect{u}}^{\operatorname{ce}}$ be the conditional expectation of the function $\widetilde{h}$ given $\standardReal_{\vect{u}}$ :

$\widetilde{h}_{\vect{u}}^{\operatorname{ce}}(\standardReal_{\vect{u}}) = \mathbb{E}_{\standardRV_{\overline{\vect{u}}}} \left[\widetilde{h}\left(\standardRV\right) | \standardRV_{\vect{u}} = \standardReal_{\vect{u}}\right]$

for any $\standardReal_{\vect{u}} \in \standardInputSpace_{\vect{u}}$ . Let $\set{J}_{\vect{u}}^{\operatorname{ce}} \subseteq \set{J}^P$ be the set of multi-indices having zero components when the marginal multi-index is not in $\vect{u}$ :

$\set{J}_{\vect{u}}^{\operatorname{ce}} = \left\{\vect{\alpha} \in \set{J}^P \; | \; \alpha_i = 0 \textrm{ if } i \not \in \vect{u}, \; i = 1, ..., \inputDim\right\}.$

This set of multi-indices defines the functions that depends on the variables in the group $\vect{u}$ and only them. For any $\vect{\alpha} \in \set{J}_{\vect{u}}^{\operatorname{ce}}$ , let $\psi_{\vect{\alpha}}^{\operatorname{ce}}$ be the orthogonal polynomial defined by :

$\psi_{\vect{\alpha}}^{\operatorname{ce}}(\standardReal_{\vect{u}}) = \begin{cases} \prod_{\substack{i = 1 \\ i \in \vect{u}}}^\inputDim \pi_{\alpha_i}^{(i)} (z_i) & \textrm{if } \alpha_i = 0 \textrm{ for any } i \not \in \vect{u}, \\ 1 & \textrm{if } \alpha_i = 0 \textrm{ for } i = 1, ..., \inputDim, \\ 0 & \textrm{otherwise}. \end{cases}$

Therefore :

$\widetilde{h}_{\vect{u}}^{\operatorname{ce}}(\standardReal_{\vect{u}}) = \sum_{\vect{\alpha} \in \set{J}_{\vect{u}}^{\operatorname{ce}}} a_{\vect{\alpha}} \psi_{\vect{\alpha}}^{\operatorname{ce}}(\standardReal_{\vect{u}})$

for any $\standardReal_{\vect{u}} \in \standardInputSpace_{\vect{u}}$ . Finally, the conditional expectation of the surrogate model is:

$\metaModel_{\vect{u}}\left(\inputReal_{\vect{u}}\right) = \widetilde{h}_{\vect{u}}^{\operatorname{ce}}(T_{\vect{u}}\left(\inputReal_{\vect{u}}\right))$

where $\standardRV_{\vect{u}} = T_{\vect{u}}(\inputRV_{\vect{u}})$ is the corresponding marginal mapping of the iso-probabilistic mapping $\standardRV = T(\inputRV)$ .

Parameters:

conditioningIndicessequence of int in [0, inputDimension - 1]: The indices $\vect{u}$ of the input random vector to condition.

Returns:

conditionalPCEFunctionalChaosResult: The functional chaos result of the conditional expectation. Its input dimension is $\operatorname{card}(\vect{u})$ and its output dimension is $\outputDim$ (i.e. the output dimension is unchanged).

getDistribution()¶

Get the input distribution.

Returns:

distributionDistribution: Distribution of the input random vector $\inputRV$ .

getErrorHistory()¶

The error history accessor.

This is only available with LARS, and when the output dimension is 1.

Returns:

errorHistorysequence of float: The error history

getIndices()¶

Get the indices of the final basis.

Returns:

indicesIndices: Indices $\set{J}^P_s$ of the elements of the multivariate basis used in the decomposition. Each integer in this list is the input argument of the EnumerateFunction. If a model selection method such as LARS is used, these indices are not contiguous.

getIndicesHistory()¶

The basis indices selection history accessor.

This is only available with LARS, and when the output dimension is 1.

Returns:

indicesHistory2-d sequence of int: The basis indices selection history, for each iteration. Each inner list gives the indices of the basis terms at i-th iteration.

getInputSample()¶

Accessor to the input sample.

Returns:

inputSampleSample: The input sample.

getInverseTransformation()¶

Get the inverse isoprobabilistic transformation.

Returns:

invTransfFunction: $T^{-1}$ such that $T(\inputRV) = \standardRV$ .

getMetaModel()¶

Accessor to the metamodel.

Returns:

metaModelFunction: Metamodel.

getName()¶

Accessor to the object’s name.

Returns:

namestr: The name of the object.

getOrthogonalBasis()¶

Get the orthogonal basis.

Returns:

basisOrthogonalBasis: Factory of the orthogonal basis.

getOutputSample()¶

Accessor to the output sample.

Returns:

outputSampleSample: The output sample.

getReducedBasis()¶

Get the reduced basis.

Returns:

basislist of Function: Collection of the functions $(\psi_k)_{k\in \set{J}^P_s}$ used in the decomposition.

getSampleResiduals()¶

Get residuals sample.

Returns:

residualsSampleSample: The sample of residuals $r_{ji} = y_{ji} - \metaModel_i(\vect{x^{(j)}})$ for $i = 1, ..., n_Y$ and $j = 1, ..., n$ .

getTransformation()¶

Get the isoprobabilistic transformation.

Returns:

transformationFunction: Transformation $T$ such that $T(\inputRV) = \standardRV$ .

hasName()¶

Test if the object is named.

Returns:

hasNamebool: True if the name is not empty.

involvesModelSelection()¶

Get the model selection flag.

A model selection method can be used to select the coefficients of the decomposition which enable to best predict the output. Model selection can lead to a sparse functional chaos expansion.

Returns:

involvesModelSelectionbool: True if the method involves a model selection method.

isLeastSquares()¶

Get the least squares flag.

Returns:

isLeastSquaresbool: True if the coefficients were estimated from least squares.

setErrorHistory(errorHistory)¶

The error history accessor.

Parameters:

errorHistorysequence of float: The error history

setInputSample(sampleX)¶

Accessor to the input sample.

Parameters:

inputSampleSample: The input sample.

setInvolvesModelSelection(involvesModelSelection)¶

Set the model selection flag.

A model selection method can be used to select the coefficients of the decomposition which enable to best predict the output. Model selection can lead to a sparse functional chaos expansion.

Parameters:

involvesModelSelectionbool: True if the method involves a model selection method.

setIsLeastSquares(isLeastSquares)¶

Set the least squares flag.

Parameters:

isLeastSquaresbool: True if the coefficients were estimated from least squares.

setMetaModel(metaModel)¶

Accessor to the metamodel.

Parameters:

metaModelFunction: Metamodel.

setName(name)¶

Accessor to the object’s name.

Parameters:

namestr: The name of the object.

setOutputSample(sampleY)¶

Accessor to the output sample.

Parameters:

outputSampleSample: The output sample.

setSelectionHistory(indicesHistory, coefficientsHistory)¶

The basis coefficients and indices accessor.

Parameters:

indicesHistory2-d sequence of int: The basis indices selection history
coefficientsHistory2-d sequence of float: The coefficients values selection history Must be of same size as indicesHistory.