Option for emitting all integrator time steps

[rruusu]

Current status

Currently OMSimulator only emits data into the result file using a fixed time step size, either based on the maximum time step size or the number of intervals provided by the --intervals option.

Feature description

It is sometimes useful to get output that shows all steps made by the variable step solver, especially for debugging purposes.

One option for expressing this to OMSimulator could be by setting --intervals=0 on the command line.

[rruusu]

Without this feature, the solver cannot take steps longer than the required output interval.

This results in:

• The solver performing unnecessary work by using time steps that are shorter than required by the given tolerances.
• The generated result files being unnecessarily large.

Example

The plot below was generated using the fix in #1522 with a rotational mechanics toy model that exhibits short transients. Each output data point is marked with a dot on the line. The simulation used a maximum time step size of 0.1 s, resulting in a CSV file size of 1243 KB.

Close-up of the first step response:

Current status

Running the same simulation using the current maintenance/v2.1 head only produces data at 0.1 s intervals, which makes the results entirely worthless:

To roughly match the temporal resolution of the example above, we must reduce the maximum time step size to 0.001 s. This increases the size of the output CSV to 9842 KB (more than 8 times larger) and causes a similar increase in the required simulation time.

[rruusu]

The toy model in the figures above also exhibits the issue in #1530, which is now also fixed by #1522.

Below is a close-up of the third step response, which should start at t = 4.5 s.

• Blue: the current head of maintenance/v2.1 using max step of 0.001 s.
• Red: the current head of Output all CVODE steps #1522 using max step of 0.1 s.

Tolerances in both cases are 1e-3 for absolute and 1e-2 for relative.

[rruusu]

The test model with Lua script and Python for plotting:

VibrationTest.zip