SimTK: OpenMM: [#828] Calling reinitialize() in OpenMMContext object also resets random number sequences

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Date:
2009-06-16 08:01

Priority:
3

State:
Open

Submitted by:
John Chodera (jchodera)

Assigned to:
Nobody (None)

Summary:
Calling reinitialize() in OpenMMContext object also resets random number sequences

Detailed description
Calling reinitialize() in OpenMMContext object also resets random number sequences of Langevin integrators or Andersen thermostats. If reinitialize() is called periodically, this will cause the same net forces to act on the system, this will cause the system to behave in strange, non-random ways, such as a protein rapidly unfolding. If this is the intended behavior, a caution should be added to the API documentation. If this is not the intended behavior, it should be changed. It must be decided whether the intention of reinitialize() is to reset all behavior back to the initial specification, or to simply push out updates to force parameters (as the documentation suggests).
Calling reinitialize() in OpenMMContext object also resets random number sequences of Langevin integrators or Andersen thermostats. If reinitialize() is called periodically, this will cause the same net forces to act on the system, this will cause the system to behave in strange, non-random ways, such as a protein rapidly unfolding. If this is the intended behavior, a caution should be added to the API documentation. If this is not the intended behavior, it should be changed. It must be decided whether the intention of reinitialize() is to reset all behavior back to the initial specification, or to simply push out updates to force parameters (as the documentation suggests).

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Date: 2009-06-16 18:22 Sender: John Chodera Once I discovered that these random seeds were being reset to the same initial value, I did indeed start feeding new random numbers via setRandomNumberSeed(). The point is that I found this behavior sufficiently non-obvious that it took many hours to figure out what was going on, so some explicit warning of this behavior in the API documentation may be warranted to save others from similar experiences.
Date: 2009-06-16 17:45 Sender: Peter Eastman Note that LangevinIntegrator and AndersenThermostat each have a setRandomNumberSeed() method that you can use to keep them from using the same random numbers each time.

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