xvi Contents
13.6 Hadamard Product of Tensors . . . .............................406
13.7 ConvolutionofTensors .....................................407
13.8 Matrix-Matrix Multiplication . . . .............................408
13.9 Matrix-Vector Multiplication . . . .............................408
13.9.1 IdenticalFormats ....................................409
13.9.2 SeparableForm(13.25a) .............................409
13.9.3 Elementary Kronecker Tensor (13.25b) . . . ..............410
13.9.4 Matrix in p-TermFormat(13.25c)......................411
13.10FunctionsofTensors,FixedPointIterations ....................412
13.11Example:OperationsforQuantumChemistryApplications .......414
14 Tensorisation ..................................................417
14.1 Basics ...................................................417
14.1.1 Notations, Choice of T
D
..............................417
14.1.2 Format H
tens
ρ
.......................................419
14.1.3 OperationswithTensorisedVectors ....................420
14.1.4 ApplicationtoRepresentationsbyOtherFormats .........421
14.1.5 Matricisation .......................................423
14.1.6 GeneralisationtoMatrices ............................423
14.2 ApproximationofGridFunctions ............................425
14.2.1 GridFunctions ......................................425
14.2.2 Exponential Sums . ..................................425
14.2.3 Polynomial Approximations for Asymptotically Smooth
Functions ..........................................426
14.2.4 Multiscale Feature and Conclusion . ...................427
14.2.5 LocalGridRefinement ...............................428
14.3 Convolution...............................................429
14.3.1 Notations ..........................................429
14.3.2 PreviewandMotivation ..............................430
14.3.3 Tensor Algebra A(
0
) ................................432
14.3.4 Algorithm ..........................................438
14.4 FastFourierTransform .....................................441
14.4.1 FFT for C
n
Vectors ..................................441
14.4.2 FFTforTensorisedVectors ...........................442
14.5 TensorisationofFunctions ..................................444
14.5.1 Isomorphism Φ
F
n
....................................444
14.5.2 Scalar Products . . . ..................................445
14.5.3 Convolution ........................................446
14.5.4 Continuous Functions . . . .............................446
15 Generalised Cross Approximation ...............................447
15.1 ApproximationofGeneralTensors ...........................447
15.1.1 ApproximationofMultivariateFunctions................448
15.1.2 Multiparametric Boundary Value Problems and PDE with
StochasticCoefficients ...............................449
15.1.3 FunctionofaTensor .................................451