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(sec-item-loadcoordinate)=
# LoadCoordinate

Load with scalar value, which is attached to a coordinate-based marker; the load can be used e.g. to apply a force to a single axis of a body, a nodal coordinate of a finite element  or a torque to the rotatory DOF of a rigid body.

## Interface

- Markers it acts on: those providing `Coordinate`: [](#sec-item-markernodecoordinate), [](#sec-item-markernodeode1coordinate), [](#sec-item-markernoderotationcoordinate), [](#sec-item-markerbodiesrelativetranslationcoordinate), [](#sec-item-markerbodiesrelativerotationcoordinate), [](#sec-item-markerbodycable2dshape), [](#sec-item-markerbodycable2dcoordinates)

## Parameters

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

| name | type | size | default | description |
|---|---|---|---|---|
| **name** | String |  | '' | load's unique name |
| **markerNumber** | MarkerIndex |  | invalid (-1) | marker's number to which load is applied |
| **load** | Real |  | 0. | (symbol: $f$) scalar load [SI:N]; in case of a user function, this value is ignored |
| **loadUserFunction** | LoadCoordinateLoadUserFunction |  | 0 | (symbol: $\mathrm{UF} \in \Rcal$) A Python function which defines the time-dependent load and replaces the load; see description below; see also notes on loadFactor and drawing in LoadForceVector! |
| **visualization** | VLoadCoordinate |  |  | parameters for visualization of item |

## Visualization parameters

`VLoadCoordinate` has no parameters.

## Drawing

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

### Load and its frame

The scalar $f$ = `load`, or the return value of `loadUserFunction`, acts on one coordinate: the one
the coordinate marker selects, e.g. `MarkerNodeCoordinate`. It has no frame of its own: it is a
generalized force in the direction of the coordinate, which is a force for a displacement coordinate
and a torque-like quantity for a rotation parameter - for Euler parameters or a slope, not a torque
in the physical sense, so take care what the coordinate means.

### Generalized forces

$$
Q_i = f
$$

for the marked coordinate $i$, and zero for all others. The load factor applies as for a force.

**Userfunction**: `loadUserFunction(mbs, t, load)`
A user function, which computes the scalar load depending on time and the object's `load` parameter.

| arguments / return | type or size | description |
|---|---|---|
| `mbs` | MainSystem | provides MainSystem mbs to which load belongs |
| `t` | Real | current time in mbs |
| `load` | Real | $\bv$ copied from object; WARNING: this parameter does not work in combination with static computation, as it is changed by the solver over step time |
| **return value** | Real | computed load |

*Example*:

```python
from math import sin, cos, pi
#this example uses the object's stored parameter load to compute a time-dependent load
def UFload(mbs, t, load):
    return load*sin(10*(2*pi)*t)

n0=mbs.AddNode(Point())
nodeMarker = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=n0,coordinate=0))
mbs.AddLoad(LoadCoordinate(markerNumber = markerCoordinate,
                           load = 10,
                           loadUserFunction = UFload))
```

(miniexample-loadcoordinate)=
## Mini example


```python
#a load on one coordinate, growing in time through its user function
node = mbs.AddNode(Node1D(referenceCoordinates=[0]))
mbs.AddObject(ObjectMass1D(nodeNumber=node, mass=1))
mCoord = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber=node, coordinate=0))
def UFload(mbs, t, load):
    return load*t
mbs.AddLoad(LoadCoordinate(markerNumber=mCoord, load=1, loadUserFunction=UFload))

mbs.Assemble()
mbs.SolveDynamic()

#q = t^3/6 at t=1
exu.sys['testResult'] = mbs.GetNodeOutput(node, exu.OutputVariableType.Coordinates) #0.1667
```


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), [`plotSensorExamples.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/plotSensorExamples.py) (Ex), [`slidercrankWithMassSpring.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/Examples/slidercrankWithMassSpring.py) (Ex), [`CoordinateSpringDamperTest.py`](https://github.com/jgerstmayr/EXUDYN/blob/master/python/TestModels/CoordinateSpringDamperTest.py) (TM)