mapreducer specifies the default global execution environment for mapreduce.

If you have Parallel Computing Toolbox installed, and your default cluster profile specifies a local cluster, then mapreducer also opens a parallel pool so that mapreduce can distribute mapper and reducer tasks to the pool workers.

You can set your parallel preferences so that a pool does not automatically open. In this case, you must explicitly start a pool if you want to use parallel resources. See Parallel Preferences.

mapreducer(0) specifies that mapreduce run in the MATLAB client session without using any parallel resources.

mapreducer(poolobj) specifies a cluster for parallel execution of mapreduce. poolobj is a parallel.Pool object. The default pool is the current pool that is returned or opened by gcp.

mapreducer(hcluster) specifies a Hadoop^® cluster for parallel execution of mapreduce. hcluster is a parallel.cluster.Hadoop object.

mapreducer(mr) sets the global execution environment for mapreduce using a previously created MapReducer object, mr, if its ObjectVisibility property is 'On'.

mr = mapreducer(___) returns a MapReducer object to specify the execution environment. You can define several MapReducer objects, allowing you to swap execution environments by passing one as an input argument to mapreduce.

mr = mapreducer(___,'ObjectVisibility','Off') hides the visibility of the MapReducer object, mr, using any of the previous syntaxes. Use this syntax to create new MapReducer objects without affecting the global execution environment of mapreduce.

If this object's ObjectVisibility property is 'On' (the default), mr defines the default global execution environment for mapreduce. If the ObjectVisibility property is 'Off', you can pass mr as an input argument to mapreduce to explicitly specify the execution environment for that particular call.