3. Classes FMUModelExchangeV1 and FMUModelExchangeV2

The most obvious obstacle for using a bare FMU for ModelExchange is its lack of an integrator. For this reason, classes FMUModelExchangeV1 and FMUModelExchangeV2 provide generic methods for the integration of FMUs for ModelExchange for FMI Version 1.0 and 2.0, respectively. Instances of these classes own the actual FMU instance and are able to advance the current state up to a specified point in time, including the proper handling of FMU-internal events. The classes also provide functionality for convenient input and output handling.

The following example demonstrates the basic usage of class FMUModelExchangeV2 (usage of class FMUModelExchangeV1 is analogous):

# create FMI++ wrapper for FMU for ModelExchange (Version 2.0)
logging_on = False
stop_before_event = False
event_search_precision = 1e-10
integrator_type = fmipp.integratorBDF
fmu = fmipp.FMUModelExchangeV2( uri_to_extracted_fmu, model_name, logging_on, stop_before_event, event_search_precision, integrator_type )

status = fmu.instantiate( "my_test_model_1" ) # instantiate model
assert status == fmipp.statusOK # check status

status = fmu.setRealValue( 'k', 1.0 ) # set value of parameter 'k'
assert status == fmipp.statusOK # check status

status = fmu.initialize() # initialize model
assert status == fmipp.statusOK # check status

t = 0.0
stepsize = 0.125
tstop = 3.0

while ( ( t + stepsize ) - tstop < 1e-6 ):
  t = fmu.integrate( t + stepsize ) # integrate model
  x = fmu.getRealValue( "x" ) # retrieve output variable 'x'

The integration algorithms provided by ODEINT and SUNDIALS can be chosen with an appropriate flag in the constructor (see example above). The following algorithms are available:

Stepper	Name	Suite	Order	Adaptive	Recommended usecases
integratorEU	Explicit Euler	ODEINT	1	No	Testing
integratorRK	4th order Runge-Kutta	ODEINT	4	No	Testing
integratorABM	Adams-Bashforth-Moulton	ODEINT	8	No	Testing
integratorCK	Cash-Karp	ODEINT	5	Yes	Nonstiff Models
integratorDP	Dormand-Prince	ODEINT	5	Yes	Nonstiff Models
integratorFE	Fehlberg	ODEINT	8	Yes	Nonstiff, smooth Models
integratorBS	Bulirsch Stoer	ODEINT	1-16	Yes	High precision required
integratorRO	Rosenbrock	ODEINT	4	Yes	Stiff Models
integratorBDF	Backward Differentiation Formula	SUNDIALS	1-5	Yes	Stiff Models
integratorABM2	Adams-Bashforth-Moulton	SUNDIALS	1-12	Yes	Nonstiff Models with expensive right hand side