Define execution environment for mapreduce or tall arrays
mapreducer, with no arguments, sets the global execution
environment to be the default: a parallel pool if you have Parallel Computing Toolbox™ available, or else the local MATLAB® session. mapreducer is a configuration
function that changes how MATLAB executes mapreduce algorithms and tall array
calculations. Use this function to set, change, or store the execution
environment to leverage Parallel Computing Toolbox, MATLAB
Parallel Server™, or MATLAB
Compiler™. If you have Parallel Computing Toolbox installed, then when you use the tall or
mapreduce functions MATLAB automatically starts a parallel pool of workers (unless you have
changed the default preferences).
Note
If no toolboxes are available, then mapreduce
algorithms and tall array calculations automatically run using the local
MATLAB session, and it is unnecessary to specify configuration
settings using mapreducer to use these features.
However, if you have Parallel Computing Toolbox, MATLAB
Parallel Server, or MATLAB
Compiler, then additional mapreducer
configuration options are available for running in parallel or deployed
environments.
For more information, see mapreducer (Parallel Computing Toolbox) in the
Parallel Computing Toolbox documentation, or mapreducer (MATLAB Compiler) in the
MATLAB
Compiler documentation.
mapreducer(0) sets the global execution
environment to be the local MATLAB session.
mapreducer( sets
the global execution environment using a previously created MapReducer
object, mr)mr.
mr = mapreducer(___)mr as a fourth input argument to mapreduce when
you want to explicitly specify the execution environment.
mr = mapreducer(___,'ObjectVisibility','Off')mr. Use this
syntax to create new MapReducer objects without affecting the global
execution environment.
When working with tall arrays, use mapreducer to
set the execution environment prior to creating the tall array with tall(ds).
Tall arrays are bound to the current global execution environment
when they are constructed. If the global execution environment is
subsequently changed, then the tall array becomes invalid and must
be reconstructed.