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(testmodels-connectoroutputvariablestest)=
# connectorOutputVariablesTest.py

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

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

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details:  Reading the output variables of connectors and joints (#2735), and what happens with one an
#           item does not declare:
#           (1) ObjectContactCoordinate: a 1D mass resting on a stop; Distance is the gap, negative in
#               contact, and the contact force holds the mass; with activeConnector=False the mass falls
#               through the stop;
#           (2) ObjectJointRevolute2D: the Displacement between the two joint points stays zero;
#           (3) ObjectJointPrismatic2D with the rotation constrained: Distance along the axis (the axis
#               need not be normalized) and Rotation, which stays zero;
#           (4) ObjectJointPrismatic2D with the rotation free: Rotation is the rotation of the body
#               relative to the ground;
#           (5) an output variable that an item does not declare raises an exception - Rotation of
#               ObjectJointRevolute2D, and ObjectContactCircleCable2D, which declares none.
#
# Author:   Johannes Gerstmayr
# Date:     2026-10-01
#
# 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
from exudyn.beams import GenerateBeamElementsAlongLine

import numpy as np

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

OV = exu.OutputVariableType
simulationSettings = exu.SimulationSettings()
simulationSettings.timeIntegration.newton.useModifiedNewton = False #Just for the test; modified Newton is usually faster
testResult = 0

def ContactCoordinate(activeConnector):
    """a 1D mass at 0.1 above a stop, pushed down by 10 N; returns the system, the node and the contact"""
    SC = exu.SystemContainer()
    mbs = SC.AddSystem()
    nGround = mbs.AddNode(NodePointGround())
    node = mbs.AddNode(Node1D(referenceCoordinates=[0], initialCoordinates=[0.1]))
    mbs.AddObject(ObjectMass1D(nodeNumber=node, mass=1))
    mCoordinate = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=node, coordinate=0))
    mGround = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=nGround, coordinate=0))
    nData = mbs.AddNode(NodeGenericData(numberOfDataCoordinates=1, initialCoordinates=[0.1]))
    oContact = mbs.AddObject(ObjectContactCoordinate(markerNumbers=[mGround, mCoordinate], nodeNumber=nData,
                                                     contactStiffness=1e4, contactDamping=100,
                                                     activeConnector=activeConnector))
    mbs.AddLoad(LoadCoordinate(markerNumber=mCoordinate, load=-10))
    mbs.Assemble()
    mbs.SolveDynamic(simulationSettings)
    return (mbs, node, oContact)

#(1) contact: at rest on the stop, the gap is the coordinate (stop at 0, no offset): -F/k = -1e-3
(mbs, node, oContact) = ContactCoordinate(True)
q = mbs.GetNodeOutput(node, OV.Coordinates)  #a float for a node with one coordinate
gap = mbs.GetObjectOutput(oContact, OV.Distance)
exu.Print('contact: coordinate', q, ', gap', gap, '(both -1e-3 at rest)')
testResult += q + gap
(mbs, node, oContact) = ContactCoordinate(False)
q = mbs.GetNodeOutput(node, OV.Coordinates)  #a float for a node with one coordinate
exu.Print('inactive contact: coordinate', q, '(falls freely: 0.1 - F/(2m) t^2 = -4.9)')
testResult += q

def Planar(addJoint):
    """a planar rigid body joined to the ground by addJoint(mbs, mGround, mBody), pushed by a force and a torque"""
    SC = exu.SystemContainer()
    mbs = SC.AddSystem()
    oGround = mbs.AddObject(ObjectGround())
    node = mbs.AddNode(NodeRigidBody2D(referenceCoordinates=[0, 0, 0]))
    body = mbs.AddObject(ObjectRigidBody2D(nodeNumber=node, mass=2, inertia=0.1))
    mGround = mbs.AddMarker(MarkerBodyRigid(bodyNumber=oGround))
    mBody = mbs.AddMarker(MarkerBodyRigid(bodyNumber=body))
    oJoint = addJoint(mbs, mGround, mBody)
    mbs.AddLoad(LoadForceVector(markerNumber=mBody, loadVector=[2, 1, 0]))
    mbs.AddLoad(LoadTorqueVector(markerNumber=mBody, loadVector=[0, 0, 0.1]))
    mbs.Assemble()
    mbs.SolveDynamic(simulationSettings)
    return (mbs, node, oJoint)

#(2) revolute joint: the joint points stay together
(mbs, node, oRevolute) = Planar(lambda mbs, m0, m1: mbs.AddObject(ObjectJointRevolute2D(markerNumbers=[m0, m1])))
displacement = mbs.GetObjectOutput(oRevolute, OV.Displacement)
exu.Print('revolute joint: displacement', displacement)
testResult += np.linalg.norm(displacement)

#(3) prismatic joint along x with the rotation constrained: x = F_x/(2m) t^2 = 0.5 at t = 1
(mbs, node, oJoint) = Planar(lambda mbs, m0, m1: mbs.AddObject(ObjectJointPrismatic2D(
    markerNumbers=[m0, m1], axisMarker0=[2, 0, 0], normalMarker1=[0, 1, 0])))
distance = mbs.GetObjectOutput(oJoint, OV.Distance)
rotation = mbs.GetObjectOutput(oJoint, OV.Rotation)
exu.Print('prismatic joint, rotation constrained: distance', distance, '(0.5), rotation', rotation)
testResult += distance + rotation

#(4) prismatic joint with the rotation free: the output Rotation is the rotation of the body
(mbs, node, oJoint) = Planar(lambda mbs, m0, m1: mbs.AddObject(ObjectJointPrismatic2D(
    markerNumbers=[m0, m1], constrainRotation=False)))
q = mbs.GetNodeOutput(node, OV.Coordinates)
rotation = mbs.GetObjectOutput(oJoint, OV.Rotation)
exu.Print('prismatic joint, rotation free: rotation', rotation, '= body rotation', q[2])
testResult += rotation + mbs.GetObjectOutput(oJoint, OV.Distance)

#(5) an output variable the item does not declare raises
refused = 0
(mbs, node, oRevolute) = Planar(lambda mbs, m0, m1: mbs.AddObject(ObjectJointRevolute2D(markerNumbers=[m0, m1])))
try:
    mbs.GetObjectOutput(oRevolute, OV.Rotation)
except Exception as error:
    exu.Print('refused:', str(error).split(' [Python file')[0])
    refused += 1

SC = exu.SystemContainer()
mbs = SC.AddSystem()
oGround = mbs.AddObject(ObjectGround())
beamInfo = GenerateBeamElementsAlongLine(mbs, positionStart=[0, 0, 0], positionEnd=[1, 0, 0],
                        numberOfElements=1, beamTemplate=ObjectANCFCable2D(massPerLength=1,
                        bendingStiffness=1, axialStiffness=100), groundConstraintsStart=[1, 1, 1, 1])
nodes, elements, *_ = beamInfo['nodes'], beamInfo['elements'], beamInfo['loads']
mCircle = mbs.AddMarker(MarkerBodyPosition(bodyNumber=oGround, localPosition=[0.5, -1, 0]))
mShape = mbs.AddMarker(MarkerBodyCable2DShape(bodyNumber=elements[0], numberOfSegments=2))
nData = mbs.AddNode(NodeGenericData(numberOfDataCoordinates=2, initialCoordinates=[0.1, 0.1]))
oContactCable = mbs.AddObject(ObjectContactCircleCable2D(markerNumbers=[mCircle, mShape], nodeNumber=nData,
                              numberOfContactSegments=2, circleRadius=0.1, contactStiffness=1e3))
mbs.Assemble()
try:
    mbs.GetObjectOutput(oContactCable, OV.Distance)
except Exception as error:
    exu.Print('refused:', str(error).split(' [Python file')[0])
    refused += 1
testResult += refused

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