<!-- GENERATED by tools/generators/examplesDocsEmitter.py from python/ - do not edit -->
(testmodels-emptysystemtest)=
# emptySystemTest.py

You can view and download this file on Github: [emptySystemTest.py](https://github.com/jgerstmayr/EXUDYN/tree/master/python/TestModels/emptySystemTest.py)

```{code-block} python
:linenos:

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details:  A system without coordinates - only a ground, a sensor and a user function - is solved by every solver
#           (#2790): the time advances, the PreStepUserFunction is called in every step and the sensor records it;
#           with the dense and with the sparse linear solver. Such a system is a starting point that grows (items
#           added later), or a model whose motion is prescribed and only measured.
#
# Author:   Johannes Gerstmayr
# Date:     2026-10-02
#
# Copyright:This file is part of Exudyn. Exudyn is free software. You can redistribute it and/or modify it under the terms of the Exudyn license. See 'LICENSE.txt' for more details.
#
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

import exudyn as exu
from exudyn.utilities import * #includes itemInterface and rigidBodyUtilities
import numpy as np

testIsActive = exu.sys.get('testIsActive', False)

DST = exu.DynamicSolverType
testResult = 0
for linearSolverType in [exu.LinearSolverType.EXUdense, exu.LinearSolverType.EigenSparse]:
    for solver in [DST.ExplicitEuler, DST.RK44, DST.ODE23, DST.GeneralizedAlpha, DST.TrapezoidalIndex2, 'static']:
        SC = exu.SystemContainer()
        mbs = SC.AddSystem()
        mbs.AddObject(ObjectGround())
        mbs.variables['steps'] = 0
        def PreStepUserFunction(mbs, t):
            mbs.variables['steps'] += 1
            return True
        mbs.SetPreStepUserFunction(PreStepUserFunction)
        sensor = mbs.AddSensor(SensorUserFunction(sensorUserFunction=lambda mbs, t, sensorNumbers, factors, configuration: [np.sin(t)],
                                                  storeInternal=True))
        mbs.Assemble()
        assert len(mbs.systemData.GetODE2Coordinates()) == 0

        simulationSettings = exu.SimulationSettings()
        simulationSettings.timeIntegration.numberOfSteps = 10
        simulationSettings.timeIntegration.endTime = 1
        simulationSettings.solution.file.write = False
        simulationSettings.linearSolver.solverType = linearSolverType
        if solver == 'static':
            mbs.SolveStatic(simulationSettings)
        else:
            mbs.SolveDynamic(simulationSettings, solverType=solver)

        data = mbs.GetSensorStoredData(sensor)
        exu.Print(str(linearSolverType).split('.')[-1], str(solver).split('.')[-1], ': steps', mbs.variables['steps'],
                  ', last time', data[-1, 0], ', rows', len(data))
        testResult += data[-1, 0] + data[-1, 1] + mbs.variables['steps']

exu.Print('solution of emptySystemTest=', testResult)
exu.sys['testResult'] = testResult
```