Specifies how many threads are to be used for parallel execution.
If Y has the value ⍬, R is the number of virtual processors in the machine.
Otherwise, Y is an integer that specifies the number of threads that are to be used henceforth for parallel execution. Prior to this call, the default number of threads is specified by the parameter APL_MAX_THREADS. See APL_MAX_THREADS.
Note that whatever the value of Y, Dyalog limits the number of threads to 64. So the effective number of threads is Y⌊64.
R is the previous value.
To set the number of threads to be the same as the number of virtual processors, execute the stamement:
{}1111⌶ 1111⌶⍬
See Parallel Execution and Parallel Execution Threshold.