MC_CORES and mc.cores for parallel package

Your error is in thinking that environment variables are the same thing as options. While environment variables might be used to set initial values of certain options, options are completely separate from environment variables.  If you want to change the option on the fly, then change the option.

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Sent from my phone. Please excuse my brevity.

On December 7, 2016 6:26:55 AM PST, Marc Girondot via R-help <r-help at r-project.org> wrote:

Hi,

From the documentation of ?options

Options set in package parallel
These will be set when package parallel (or its namespace) is loaded if

not already set.

mc.cores:
a integer giving the maximum allowed number of additional R processes
allowed to be run in parallel to the current R process. Defaults to the

setting of the environment variable MC_CORES if set. Most applications
which use this assume a limit of 2 if it is unset.

Then I try:

getOption("mc.cores")

NULL

I suspect that my environment variable MC_CORES is not set. I test and
that's right:

Sys.getenv("MC_CORES")

[1] ""

Then I do:

Sys.setenv(MC_CORES=4)
Sys.getenv("MC_CORES")

[1] "4"

But when I try again getOption("mc.cores"); it does not change:

getOption("mc.cores")

NULL

Probably I do something wrong but I don't see what !

Thanks

Marc