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optimad / bitpit

Open source library for scientific HPC
http://optimad.github.io/bitpit/
GNU Lesser General Public License v3.0
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LA: allow to set the block size of the linear systems #367

Closed andrea-iob closed 1 year ago

andrea-iob commented 1 year ago

Rather than working with individual elements in the matrix, it is possible to employ blocks of elements. The size of the blocks can be defined during assembly. When a size different that one is provided, the matrix will store elements by fixed-sized dense nb × nb blocks, where nb is the size of the blocks. Blocking may be advantageous when solving PDE-based simulations that leads to matrices with a naturally blocked structure (with a block size equal to the number of degrees of freedom per cell).

andrea-iob commented 1 year ago

Using block matrices can increase performances of PETSc matrix-vector product and PETSc triangular solves obtained from an ILU(0) factorization more than 50% (see https://petsc.org/release/developers/matrices/).