Execute code in parallel on workers of parallel pool
spmd, statements, end
spmd(n), statements, end
spmd(m,n), statements, end
The general form of an spmd (single program,
multiple data) statement is:
spmd
statements
endspmd, statements, end defines an spmd statement
on a single line. MATLAB® executes the spmd body
denoted by statements on several MATLAB workers
simultaneously. The spmd statement can be used
only if you have Parallel Computing Toolbox. To execute the statements
in parallel, you must first open a pool of MATLAB workers using parpool or have your parallel prefences
allow the automatic start of a pool.
Inside the body of the spmd statement, each MATLAB worker
has a unique value of labindex,
while numlabs denotes the
total number of workers executing the block in parallel. Within the
body of the spmd statement, communication functions
for communicating jobs (such as labSend and labReceive) can transfer data between
the workers.
Values returning from the body of an spmd statement
are converted to Composite objects
on the MATLAB client. A Composite object contains references
to the values stored on the remote MATLAB workers, and those
values can be retrieved using cell-array indexing. The actual data
on the workers remains available on the workers for subsequent spmd execution,
so long as the Composite exists on the client and the parallel pool
remains open.
By default, MATLAB uses as many workers as it finds available in the pool. When there are no MATLAB workers available, MATLAB executes the block body locally and creates Composite objects as necessary.
spmd(n), statements, end uses n to
specify the exact number of MATLAB workers to evaluate statements,
provided that n workers are available from the
parallel pool. If there are not enough workers available, an error
is thrown. If n is zero, MATLAB executes the
block body locally and creates Composite objects, the same as if there
is no pool available.
spmd(m,n), statements, end uses a minimum
of m and a maximum of n workers
to evaluate statements. If there are not enough
workers available, an error is thrown. m can be
zero, which allows the block to run locally if no workers are available.
For more information about spmd and Composite
objects, see Distributed Arrays and SPMD.
Perform a simple calculation in parallel, and plot the results:
parpool(3) spmd % build magic squares in parallel q = magic(labindex + 2); end for ii=1:length(q) % plot each magic square figure, imagesc(q{ii}); end delete(gcp)