[molpro-user] Behavior of -t is not identical to export OMP_NUM_THREADS

Reuti reuti at staff.uni-marburg.de
Fri Mar 2 14:19:24 CET 2018


the "molpro" script to start the application states:

[-t  omp-num-threads n]
Specify the number of OpenMP threads, as if the environment variable
 were set to n.

This seems not to happen. The reason is, that one has to `export` OMP_NUM_THREADS to make it available to the script to start Molpro, while "-t" sets the variable just locally and never exports it. The behavior is:

- exporting OMP_NUM_THREADS beforehand and running the application in parallel might lead to a quadratic number of processes/threads on the CPU

- using -t on the other hand, will just forward the value to called application (like `mrcc`), but runs each process in serial

It looks like a threaded version of the mathematical library was linked into the application. Hence the preferred startup seems to be to use "-t" solely.

Question: is the value of "-t" anywhere else used in Molpro besides exporting the set number to a called external application like `mrcc`?

-- Reuti

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