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The BLACS (Basic Linear Algebra Communication Subprograms) are a message-passing library designed for linear algebra and are the message-passing protocol used within ScaLAPACK.

The computational model consists of a one- or two-dimensional process grid, where each process stores pieces of the matrices and vectors. The BLACS include synchronous send/receive routines to communicate a matrix or submatrix from one process to another, to broadcast submatrices to many processes, or to compute global reductions (sums, maxima and minima). There are also routines to construct, change, or query the process grid. Since several ScaLAPACK algorithms require broadcasts or reductions among different subsets of processes, the BLACS permit a process to be a member of several overlapping or disjoint process grids, each one labeled by a ``context''. Some message-passing systems, such as MPI, also include this context concept; MPI calls this a ``communicator''. The BLACS provide facilities for safe inter-operation of system contexts and BLACS contexts.

Currently, the BLACS have been efficiently ported on machine-specific message-passing libraries such as the IBM (MPL) and Intel (NX) message-passing libraries, as well as more generic interfaces such as MPI and PVM. The BLACS overhead has been shown to be negligible.

Current Version:   1.1

License Type:   Free

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Targeted Platforms:

The BLACS are portable across a wide range of architectures such as the Cray T3E, IBM SP2, Intel Paragon, SGI Power Challenge, TM CM-5, networks of computers, and any system for which MPI or PVM is available.

Software/Hardware Requirements:

One of the following message-passing libraries: MPI, PVM, MPL, NX, or CMMD

Other Links: (Further details of BLACS in this LAPACK Working Note)

Mailing Lists/USENET News Groups: for more information.

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