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This has two essential differences from the first BT benchmark
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Firstly the fourth order dissipation terms are kept in the implicit (LHS) part of the equations
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Remember these were only kept in explicit right hand side for first BT benchmark
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This step makes ADI equations PENTAdiagonal (2 nonzeros each side of diagonal) as opposed to TRIdiagonal in BT
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Next step is an approximation to the resultant 5 by 5 matrices on LHS in 3 ADI sweeps. These are approximately diagonalized in a manner described in paper which ignores smaller operators and dependence of diagonalization on position
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This converts 5 by 5 BLOCK Tridiagonal matrices into a set of 1 by 1 (scalar) Pentadiagonal equations
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General parallel analysis is similar to BT as still ADI but probably less computation per communication and so lower efficiency.
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