Note: To use parallel computing as described in this chapter, you must have a Parallel Computing Toolbox™ license. |
You can use any of the Statistics and Machine Learning Toolbox™ functions with Parallel Computing Toolbox constructs
such as parfor
and spmd
. However, some functions, such
as those with interactive displays, can lose functionality in parallel.
In particular, displays and interactive usage are not effective on
workers (see Vocabulary for Parallel Computation).
Additionally, the following functions are enhanced to use parallel
computing internally. These functions use parfor
internally
to parallelize calculations.
The following functions for fitting multiclass models for support vector machines and other classifiers are also enhanced to use parallel computing internally.
Methods of the class ClassificationECOC
:
Methods of the class CompactClassificationECOC
Methods of the class ClassificationPartitionedECOC
This chapter gives the simplest way to use these enhanced functions
in parallel. For more advanced topics, including the issues of reproducibility
and nested parfor
loops, see the other sections
in this chapter.
For information on parallel statistical computing at the command line, enter
help parallelstats
To have a function compute in parallel:
To run a statistical computation in parallel, first set up a parallel environment.
Note: Setting up a parallel environment can take several seconds. |
For a multicore machine, enter the following at the MATLAB^{®} command line:
parpool(n)
n
is the number of workers you want
to use.
Create an options structure with the statset
function.
To run in parallel, set the UseParallel
option
to true
:
paroptions = statset('UseParallel',true);
Call your function with syntax that uses the options structure. For example:
% Run crossval in parallel cvMse = crossval('mse',x,y,'predfun',regf,'Options',paroptions); % Run bootstrp in parallel sts = bootstrp(100,@(x)[mean(x) std(x)],y,'Options',paroptions); % Run TreeBagger in parallel b = TreeBagger(50,meas,spec,'OOBPred','on','Options',paroptions);
For more complete examples of parallel statistical functions, see Parallel Treebagger and Examples of Parallel Statistical Functions.
After you have finished computing in parallel, close the parallel environment:
delete mypool
Tip To save time, keep the pool open if you expect to compute in parallel again soon. |
To run the example Regression of Insurance Risk Rating for Car Imports Using TreeBagger in parallel:
Set up the parallel environment to use two cores:
mypool = parpool(2) Starting parpool using the 'local' profile ... connected to 2 workers. mypool = Pool with properties: AttachedFiles: {0x1 cell} NumWorkers: 2 Cluster: [1x1 parallel.cluster.Local] SpmdEnabled: 1
Set the options to use parallel processing:
paroptions = statset('UseParallel',true);
Load the problem data and separate it into input and response:
load imports-85; Y = X(:,1); X = X(:,2:end);
Estimate feature importance using leaf size 1
and 1000
trees
in parallel. Time the function for comparison purposes:
tic b = TreeBagger(1000,X,Y,'Method','r','OOBVarImp','on',... 'cat',16:25,'MinLeaf',1,'Options',paroptions); toc Elapsed time is 16.696336 seconds.
Perform the same computation in serial for timing comparison:
tic b = TreeBagger(1000,X,Y,'Method','r','OOBVarImp','on',... 'cat',16:25,'MinLeaf',1); % No options gives serial toc Elapsed time is 21.747950 seconds.
Computing in parallel took about 75% of the time of computing serially.