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(sec-item-markernodecoordinate)=
# MarkerNodeCoordinate

A node-Marker attached to a {ref}`ODE2 <ODE2>` coordinate of a node; this marker allows to connect a coordinate-based constraint or connector to a nodal coordinate (also NodeGround); for {ref}`ODE1 <ODE1>` coordinates use `MarkerNodeODE1Coordinate`.

## Interface

- Provides: `Coordinate`
- Connectors, constraints and loads that can use it: [](#sec-item-objectconnectorcoordinatespringdamper), [](#sec-item-objectconnectorcoordinatespringdamperext), [](#sec-item-objectconnectorcoordinate), [](#sec-item-objectcontactcoordinate), [](#sec-item-loadcoordinate)

## Parameters

The parameters of the item; in a dictionary, its type is 'NodeCoordinate':

| name | type | size | default | description |
|---|---|---|---|---|
| **name** | String |  | '' | marker's unique name |
| **nodeNumber** | NodeIndex |  | invalid (-1) | node number to which marker is attached to |
| **coordinate** | UInt |  | invalid (-1) | coordinate of node to which marker is attached to; **must be given**: the default is only a placeholder |
| **visualization** | VMarkerNodeCoordinate |  |  | parameters for visualization of item |

## Visualization parameters

`VMarkerNodeCoordinate` has no parameters.

## Drawing

The item draws nothing.
(description-markernodecoordinate)=
## Detailed description

### Marker quantities

| quantity | symbol | as computed |
|---|---|---|
| coordinate | $c = q_i$ | the **current** {ref}`ODE2 <ODE2>` coordinate `coordinate` $= i$ of the node, **without** its reference value |
| its velocity | $\dot c = \dot q_i$ | the time derivative of that coordinate |

### Jacobians

$\Jm = \ev_i\tp$, a row of the unit matrix: a force $f$ acts on coordinate $i$ only, $Q_i = f$.

On a node without {ref}`ODE2 <ODE2>` coordinates - `NodePointGround` - the coordinate is zero and the
Jacobian empty, so nothing acts: this is the ground side of a `CoordinateSpringDamper` or a
`CoordinateConstraint`.

(miniexample-markernodecoordinate)=
## Mini example


```python
#one coordinate of a node: a coordinate spring between the ground node and a 1D mass
node = mbs.AddNode(Node1D(referenceCoordinates=[0]))
mbs.AddObject(ObjectMass1D(nodeNumber=node, mass=1))
mCoord = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=node, coordinate=0))
mGround = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=nGround, coordinate=0))
mbs.AddObject(ObjectConnectorCoordinateSpringDamper(markerNumbers=[mGround, mCoord], stiffness=100))
mbs.AddLoad(LoadCoordinate(markerNumber=mCoord, load=10))

mbs.Assemble()
mbs.SolveStatic()

#the spring is stretched by F/k
exu.sys['testResult'] = mbs.GetNodeOutput(node, exu.OutputVariableType.Coordinates) #0.1
```


Examples (Ex) and TestModels (TM) that show this item, with weblink to github: [`tutorialSpringDamper.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/notebooks/tutorialSpringDamper.py) (Ex), [`coordinateSpringDamper.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/coordinateSpringDamper.py) (Ex), [`SliderCrank.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/SliderCrank.py) (Ex), [`plotSensorExamples.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/plotSensorExamples.py) (Ex), [`SpringDamperMassUserFunction.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/SpringDamperMassUserFunction.py) (Ex)