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NAME

SYNOPSIS

```          link e1 e2 nl [-b break] [-l rest] [-s stiff]
```

DESCRIPTION

link creates nl elastic links between entity e1 and entity e2. The links are created so that there is at most one link connecting each point on entity e1 to a point on entity e2 and vice-versa. The links are created between the closest pair of non-linked immersed boundary points. Note that immersed boundary points may have more than one link only if the links are to distinct entities.

link requires three arguments. These are:

• e1 - the name of one of the linked entities.
• e2 - the name of the other linked entity.
• nl - the number of links between the two entities.
To link two entities, they must each be named. Therefore, in the definition of those entities, the -N or -A flags must be used.

• -b break = link breaking length(as a fraction of the initial length)
• -l rest = link resting length (as a fraction of the initial length)
• -s stiff = stiffness of the elastic springs

EXAMPLE

```          circle 0.25 1.25 0.05 -N 1
circle 0.15 1.25 0.05 -N 2
link 1 2 4 -b 4.0
```
This code establishes four links between the two circles that break when the length of the links stretchs past 4 times the initial length of the link. The resting length of these links is the initial length of the link.

The four links are created between 4 distinct pairs of immersed boundary points, and the pairs consist of one immersed boundary point on each entity. The pairs are selected so that the links are the shortest possible.

NOTE

The algorithm to find the link locations is an O(nl)2 method, but it is used only at startup. Therefore, as nl grows, the startup time increases, so be patient. To preview the IBIS file, use nl small, then increase nl as needed for the simulation.

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David Eyre
6/19/1998