id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
5470	Incorrect assumption of OMC solver on minimum time step should be removed	Francesco Casella	Karim Adbdelhak	"The model [https://libraries.openmodelica.org/branches/newInst/Modelica_3.2.3/files/Modelica_3.2.3_Modelica.Electrical.Spice3.Examples.Inverter.diff.html Modelica.Electrical.Spice3.Examples.Inverter] currently does not pass the verification phase because of serious mismatch of the output w.r.t. the reference file.

The model has the following experiment annotation:
{{{
  experiment(
      StopTime=1e-11,
      Interval=5e-15,
      Tolerance=1e-7)
}}}
The following [https://libraries.openmodelica.org/branches/newInst/Modelica_3.2.3/files/Modelica_3.2.3_Modelica.Electrical.Spice3.Examples.Inverter.sim warning] is reported by the default solver (DASSL)
{{{
Regular simulation: ./Modelica_3.2.3_Modelica.Electrical.Spice3.Examples.Inverter -abortSlowSimulation -alarm=480   -emit_protected
stdout | warning | The step-size 2.50125e-15 is too small. Adjust the step-size to 1e-12.
}}}

In fact, I get this very same message no matter what solver I select, so I suspect the ""step size"" may actually be the reporting interval; I also guess this limitation is enforced prior to the invocation of the specific solver. 

Now, the time scale of this simulation is extremely short. Time constants of transistors are in the pico-second range (1e-12 s), and the entire simulation only lasts 1e-11 s, with a resolution of 5e-15, and a fairly tight tolerance of 1e-7. In this case, one expects both time step lengths and reporting intervals which may be way shorter than 1e-12.

Although it may be sensible to have a lower limit on the step time, this should be obtained based on the simulation time scale and on the simulated system dynamics. Putting an arbitrary limit at 1e-12 is questionable, and in fact makes the results of this simulation very inaccurate.

I would suggest to simply remove this check and let each specific solver judge on wheter the time step is too short or not, based on whatever state-of-the-art heuristics it may use."	defect	closed	blocker	1.14.0	Run-time		fixed		Lennart Ochel Andreas Heuermann