**PERTURB**

This command moves node coordinates in the following manner.

Three pairs of random numbers between 0 and 1 are generated. These pairs refer to the x, y and z coordinates of the nodes respectively. The first random number of each pair is multiplied by the factor given in the command. The second random number is used to determine if the calculated offset is to be added or subtracted from the coordinate.

WARNING: No checking is done to see if elements are inverted by this perturbation. If one uses too large a value for the perturbation, one can easily cause element inversions that will flip the normal vector of triangles and cause 3D cells to have negative volumes.

**FORMAT:**

**perturb/pset,get,psetname**/xfactor,yfactor,zfactor

EXAMPLES

```
perturb/1,0,0/0.5,0,0
```

add offsets to only the xcoordinates of all nodes

```
perturb/pset,get,mypset/0.001,0.001,0.001
```

add small offsets to all coordinates of the nodes in the **pset** named *mypset.*