Dear Juan,

I want to define the recombination rate R as a function of position in the device volume.

How to write the expression? For example, if considering the R=x^{2} where R is a Node variable.

Dear Juan,

I want to define the recombination rate R as a function of position in the device volume.

How to write the expression? For example, if considering the R=x^{2} where R is a Node variable.

Dear Juan,

Thanks for your help! It is worked.

I have another question. If R=x^{2} where R is an Edge Variable, using x,y,z directly is not worked.

How to get the position information？( like (x@n0 + x@n1)/2 ? )

Best,

Tao

To create the position on the middle edge, the following two forms would work:

```
edge_average_model(device=device, region=region, node_model="x", edge_model="xmid")
```

which creates the `xmid`

model.

Alternatively

```
edge_from_node_model(device=device, region=region, node_model="x")
edge_model(device=device, region=region, name="xmid", equation="(x@n0 + x@n1)/2")
```

which creates `x@n0`

and `x@n1`

edge models needed for `xmid`

.

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