I am trying to create a 3D ABM using agents.jl. I am stuck with a very simple issue, I cannot add agents to the GridSpace. I just want to give each agent a random starting point in 3D space.

I have cannibalised the wolf-sheep and the 3D Mixed-Agent Ecosystem with Pathfinding example models, to cerate a reproducible example, the below code works if `dim = (20,20)`

, but not if `dim = (20,20,20)`

.

I initially tried adding an agent simply using `add_agent!()`

but I couldn’t get that to work, so following the 3D Mixed-Agent Ecosystem with Pathfinding example I used the `AStar()`

pathfinding function used to add hawks (seems unnecessary since I just want a random starting position and nowhere is restricted space), but that didn’t work either. I keep getting the error message:

```
ERROR: MethodError: Cannot `convert` an object of type
Tuple{Int64{},Int64{},Int64} to an object of type
Tuple{Int64{},Int64{}}
```

The error occurs in the `# Add agents`

block of code. Any advice would be great!

Reproduceable example:

```
using Agents, Agents.Pathfinding
using Random
using InteractiveDynamics
using GLMakie
# sheep agents with no traits (other than id and pos)
@agent Sheep GridAgent{2} begin
end
function initialize_model(;
n_sheep = 10,
dims = (20, 20, 20),
seed = 23182,
)
rng = MersenneTwister(seed)
space = GridSpace(dims, periodic = false)
# define where "sheep" can walk - everywhere
# land_walkmap = BitArray(trues(dims...))
# model properties
properties = (
landfinder = AStar(space; diagonal_movement = true),
#landfinder = AStar(space; walkmap = land_walkmap),
#landfinder = AStar(space; walkmap = land_walkmap, cost_metric = MaxDistance{3}(), diagonal_movement = true),
fully_grown = falses(dims),
)
model = ABM(Sheep, space; properties, rng, scheduler = Schedulers.randomly, warn = false
)
# Add agents
for _ in 1:n_sheep
add_agent_pos!(
Sheep(
nextid(model),
random_walkable(model, model.landfinder),
),
model,
)
end
# Add grass with random initial growth
for p in positions(model)
fully_grown = rand(model.rng, Bool)
model.fully_grown[p...] = fully_grown
end
return model
end
# sheep movement - random
function sheepwolf_step!(sheep::Sheep, model)
walk!(sheep, rand, model)
end
# grass - something mundane
function grass_step!(model)
for p in positions(model)
model.fully_grown[p...] = true
end
end
# set up model - fails
sheepwolfgrass = initialize_model()
```