7. Class RollbackFMU

Class RollbackFMU implements an easy way to reset the state of a given FMU for ModelExchange (FMI Version 1.0 and 2.0) to a state according to a previous time step.

Assume that at time t0 the function call integrate( t1 ) was issued, i.e., the integration of the associated FMU from time t0 to time t1 > t0. In case there happend no event during the integration, after the function call the internal state of the FMU corresponds to time t1. Now, in order to rollback the FMU to a state corresponding to time t2, with t0 < t2 < t1, the function call integrate( t2 ) is sufficient. Internally, class RollbackFMU stores a rollback state. No rollbacks corresponding to a time previous to that internally stored rollback state are possible. If not otherwise instructed, the latest stored rollback state is overwritten with the current state, in case the integration endpoint is in the future. However, the method saveCurrentStateForRollback enforces the current state to be stored as rollback state until it is explicitly released with method releaseRollbackState. This allows to make a rollback over more than one time-consecutive integration cycle.

The following example demonstrates the basic usage of class RollbackFMU:

logging_on = False
fmu = fmipp.RollbackFMU( uri_to_extracted_fmu, model_name )

instance_name = 'zigzag1'
status = fmu.instantiate( instance_name )
assert status == fmipp.statusOK

status = fmu.setRealValue( 'k', 1.0 )
assert status == fmipp.statusOK

status = fmu.initialize()
assert status == fmipp.statusOK

time = 0.0
step_size = 0.025
stop_time = 0.5
x = -1.0

while ( ( time + step_size ) - stop_time < 1e-6 ):
  # Make integration step.
  fmu.integrate( time + step_size )

  # Enforce rollback.
  fmu.integrate( time + 0.5*step_size )
  time = fmu.integrate( time + step_size )
  x = fmu.getRealValue( 'x' )