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(testmodels-coordinatespringdampertest)=
# CoordinateSpringDamperTest.py

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

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

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details:  The same mass point as `CartesianSpringDamperTest`, held by three `CoordinateSpringDamper`
#           connectors instead - one per coordinate, the first one loaded. The two results differ in
#           the last digits because this one carries an offset.
#           The model compares against a reference value written into it, so its
#           result is that difference and its reference solution is 0 (#2632).
#
# Author:   Johannes Gerstmayr
# Date:     2019-11-01, reworked 2026-09-24
#
# 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 exudyn.graphics as graphics

testIsActive = exu.sys.get('testIsActive', False)
exu.sys['testTolerance'] = 4e-13 #the tolerance RunAllModelUnitTests used for these ten

SC = exu.SystemContainer()
mbs = SC.AddSystem()

L=0.5
mass = 1.6
k = 4000
omega0 = 50 # sqrt(4000/1.6)
dRel = 0.05
d = dRel * 2 * 80 #80=sqrt(1.6*4000)
u0=-0.08
v0=1
f = 80
x0 = f/k
fFriction = 20 #force in Newton, only depends on direction of velocity

#node for mass point:
n1=mbs.AddNode(Point(referenceCoordinates = [L,0,0], initialCoordinates = [u0,0,0], initialVelocities= [v0,0,0]))
nGround=mbs.AddNode(NodePointGround(referenceCoordinates = [L,0,0]))

#add mass points and ground object:
objectGround = mbs.AddObject(ObjectGround(referencePosition = [0,0,0]))
massPoint = mbs.AddObject(MassPoint(mass = mass, nodeNumber = n1))

#marker for constraint / springDamper
groundCoordinateMarker = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber= nGround, coordinate = 0))
nodeCoordinateMarker0  = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber= n1, coordinate = 0))
nodeCoordinateMarker1  = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber= n1, coordinate = 1))
nodeCoordinateMarker2  = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber= n1, coordinate = 2))

#Spring-Dampers
mbs.AddObject(CoordinateSpringDamper(markerNumbers = [groundCoordinateMarker, nodeCoordinateMarker0], 
                                     stiffness = k, damping = d) ) #changed 2023-01-21: dryFriction=0*fFriction, dryFrictionProportionalZone=0.01)) #offset must be zero, because coordinates just represent the displacements
mbs.AddObject(CoordinateSpringDamper(markerNumbers = [groundCoordinateMarker, nodeCoordinateMarker1], stiffness = k)) 
mbs.AddObject(CoordinateSpringDamper(markerNumbers = [groundCoordinateMarker, nodeCoordinateMarker2], stiffness = k)) 

#add loads:
mbs.AddLoad(LoadCoordinate(markerNumber = nodeCoordinateMarker0, load = f))

mbs.Assemble()

simulationSettings = exu.SimulationSettings()
tEnd = 1 #1
steps = 1000    #1000
simulationSettings.solution.file.writePeriod = 1e-3
simulationSettings.timeIntegration.numberOfSteps = steps
simulationSettings.timeIntegration.endTime = tEnd
simulationSettings.show.statistics = False

simulationSettings.timeIntegration.generalizedAlpha.spectralRadius = 1 #SHOULD work with 0.9 as well
simulationSettings.solution.file.write=False

if not testIsActive: 
    SC.renderer.Start()

mbs.SolveDynamic(simulationSettings)

if not testIsActive: 
    SC.renderer.DoIdleTasks()
    SC.renderer.Stop() #safely close rendering window!

u = mbs.GetNodeOutput(n1, exu.OutputVariableType.Position)
uCoordinateSpringDamper= u[0] - L
if True:
    errorCoordinateSpringDamper = uCoordinateSpringDamper - 0.011834933407061654 #until 2022-01-25 (changed jacobians): 0.01183493340619235 #2021-09-27: new JacobianODE2RHS
    #errorCoordinateSpringDamper = uCoordinateSpringDamper -0.011834933407368853 #2021-02-04: 0.011834933407368853
else:
    errorCoordinateSpringDamper = uCoordinateSpringDamper - 0.011834933406690284 #15.12.2019: 0.011834933406690284; beofre 15.12.2019: 0.011834933407047 #for 1000 steps, endtime=1; this is different from CartesianSpringDamper because of offset L (rounding errors around 1e-14)


exu.Print('solution CoordinateSpringDamper=',uCoordinateSpringDamper)
testResult = abs(errorCoordinateSpringDamper)
exu.Print('solution of CoordinateSpringDamperTest=', testResult)
exu.sys['testResult'] = testResult
```