Parallel package
The Parallel execution package provides utilities to work with clusters, but also functions to parallelize work among cores of a single machine.
To install: pkg install -forge parallel
And then, once on each octave session, pkg load parallel
Contents
multicore parallelization (parcellfun, pararrayfun)[edit]
See also the NDpar package, for an extension of these functions to N-dimensional arrays
calculation on a single array[edit]
Code: simple |
# fun is the function to apply fun = @(x) x^2; vector_x = 1:10; vector_y = pararrayfun(nproc, fun, vector_x) |
should output
parcellfun: 10/10 jobs done
vector_y =
1 4 9 16 25 36 49 64 81 100
nproc
returns the number of cpus available (number of cores or twice as much with hyperthreading). One can use nproc - 1
instead, in order to leave one cpu free for instance.
fun
can be replaced by @myfun
if the function resides in the myfun.m
file.
In the previous example, the function was executed once for each element of the input vector_x
.
If the function is vectorized (can act on a vector and not just on scalar input), then it can be much more efficient to use the "Vectorized", true
option.
Code: vectorized |
# fun is the function to apply, vectorized (see the dot) fun = @(x) x.^2; vector_x = 1:10; vector_y = pararrayfun(nproc, fun, vector_x, "Vectorized", true, "ChunksPerProc", 1) |
should output
parcellfun: 4/4 jobs done
vector_y =
1 4 9 16 25 36 49 64 81 100
The "ChunksPerProc"
option is mandatory with "Vectorized", true
. 1
means that each proc will do its job in one shot (chunk). This number can be increased to use less memory for instance. A higher number of "ChunksPerProc"
allows also more flexibility in case of long calculations on a busy machine. If one cpu has finished all its jobs, it can take over the pending jobs of another.
Output in cell arrays[edit]
The following sample code was an answer to this question. The goal was to diagonalize 2x2 matrices contained as rows of a 2d array (each row of the array being a flattened 2x2 matrix).
Code: diagonalize NxN matrices contained in an array |
A = [0.6060168 0.8340029 0.0064574 0.7133187; 0.6325375 0.0919912 0.5692567 0.7432627; 0.8292699 0.5136958 0.4171895 0.2530783; 0.7966113 0.1975865 0.6687064 0.3226548; 0.0163615 0.2123476 0.9868179 0.1478827]; N = 2; [eigenvectors, eigenvalues] = pararrayfun(nproc, @(row_idx) eig(reshape(A(row_idx, :), N, N)), 1:rows(A), "UniformOutput", false) |
With "UniformOutput", false
, the outputs are contained in cell arrays (one cell per slice). In the sample above, both eigenvectors
and eigenvalues
are 1x5
cell arrays.
cluster operation[edit]
Documentation can be found in the README.parallel
or README.bw
files, located inside the doc
directory of the parallel package.