Object:GappyPOD

under GappyPOD {
    MinDimensionGreedyAlgorithm = mindimensiongreedyalgorithm-int;
    MaxDimensionGreedyAlgorithm = maxdimensiongreedyalgorithm-int;
    DimensionGreedyAlgorithmFactor = dimgreedyalgorithmfactor-real;
    MinSampleNodes = minsamplenodes-int;
    MaxSampleNodes = maxsamplenodes-int;
    SampleNodesFactor = samplenodesfactor-real;
    GreedyData = greedydata-id;
    GreedyLeastSquaresSolver = greedyleastsquaressolver-id;
    PerformGNATPrepro = performgnatprepro-flag;
    PseudoInverseLeastSquaresSolver = pseudoinverseleastsquaressolver-id;
    MinimumNumberSampleNodesOnFarfield = minnumbersamplenodesonfarfield-int;
    MinimumFractionSampleNodesOnSurface = minfractionsamplenodesonsurface-real;
    MinimumFractionSampleNodesInTargetRegion = minfractionsamplenodesintargetregion-real;
    under ReducedMeshTargetRegions { ... }     
}

with

mindimensiongreedyalgorithm-int [1]:
Minimum number of POD vectors to use in the greedy mesh sampling algorithm.

maxdimensiongreedyalgorithm-int [–]:
Maximum number of POD vectors to use in the greedy mesh sampling algorithm.

dimgreedyalgorithmfactor-real [1.0]:
Alternative way to specify the number of POD vectors to use in the greedy mesh sampling algorithm, specified as dimgreedyalgorithmfactor-real $\times$ total number of available POD vectors, given by the dimension of the corresponding ROB being used as specified by GreedyData.

minsamplenodes-int [1]:
minimum number of sample cells to select in the greedy mesh sampling procedure.

maxsamplenodes-int [–]:
Maximum number of sample cells to select in the greedy mesh sampling procedure.

samplenodesfactor-real [1.0]:
Maximum number of sample cells to select in the greedy mesh sampling procedure. If not specified, this value is set to the number of cells in the high-dimensional mesh.

greedydata-id [ResidualROB]:
Controls which ROB to use as input to the greedy mesh sampling algorithm for selecting the sample mesh cells.

ResidualROB
In this case, an ROB for the residual constructed previously (see NonlinearRomPreprocessing.ConstructROB.ResidualROB) is read from disk and used for the mesh sampling.

StateROB
In this case, the state ROB is read from disk and used for the mesh sampling. In the case where a local subspace approximation is employed, this option is not supported and it is recommended that the user construct a residual ROB for hyperreduction training and specify GreedyData = ResidualROB.

greedyleastsquaressolver-id [QR]:
Controls which algorithm is used to solve the least-squares problem arising at each iteration of the greedy mesh sampling algorithm.

QR
The least-squares solution is obtained using a QR factorization approach. This option requires compilation with the ScaLAPACK libraries.

NormalEquations
The normal equations are used to solve each arising least-squares problem.

performgnatprepro-flag [False]:
This flag controls whether to compute and write to disk the gappy POD matrix associated with the GNAT hyperreduction method when preprocessing for a GNAT-based hyperreduced ROM.

True
Compute the GNAT gappy POD matrix.

False
Do not compute the GNAT gappy POD matrix.

pseudoinverseleastsquaressolver-id [QR]:
Controls which algorithm is used to compute the Moore-Penrose pseudoinverse as required by the gappy POD matrix. This option is only relevant when PerformGNATPrepro = True.

QR
The Moore-Penrose pseudoinverse of a matrix is obtained using a QR factorization approach. This option requires compilation with the ScaLAPACK libraries.

NormalEquations
The normal equations are used to solve for the Moore-Penrose pseudoinverse of a matrix.

minnumbersamplenodesonfarfield-int [1]:
At least this many cells will be sampled from farfield boundaries in the high-dimensional mesh and included in the reduced mesh.

minfractionsamplenodesonsurface-real [–]:
At least this fraction of the sampled cells will lie on wall boundary surfaces of the high-dimensional mesh.

minfractionsamplenodesintargetregion-real [–]:
At least this fraction of the sampled cells will lie within the target regions specified under ReducedMeshTargetRegions.

ReducedMeshTargetRegions:
If desired, this object is used to specify target regions of the high-dimensional mesh to sample from when constructing the reduced mesh. The format for this object is identical to that of Space.Fixes.