Working with Single Agents

To support complex extensions of the base model, we implemented a way to retrieve single agents from containers of multiple instances having a SoA (Struct-Of-Arrays) layout under the hood.

In practice, this allows to operate on agents as if they were single structs. Let's see how this unfolds with a concrete example. As usual, we create a model instance with

import BeforeIT as Bit

parameters = Bit.AUSTRIA2010Q1.parameters
initial_conditions = Bit.AUSTRIA2010Q1.initial_conditions
model = Bit.Model(parameters, initial_conditions);

Three containers in this model have multiple instances of agents: model.firms, model.w_act, model.w_inact. Each of them to be compatible with this approach contains IDs which correspond to single instances. IDs are UInt and are set internally.

Note

One invariant of IDs one could rely on is that at initialization IDs are mapped one-to-one to indices of the arrays. Though, if any deletion happens this won't be true anymore.

id = 1
agent = model.w_act[id]

Agent{Workers}(ID = 1, Y_h = 0.7661282859097249, D_h = 3.7818066335944875, K_h = 6.973481059156251, w_h = 0.2697101055708983, O_h = 1, C_d_h = 0.0, I_d_h = 0.0, C_h = 0.0, I_h = 0.0)

Then we can access or modify attributes of the agent simply with

agent.Y_h

0.7661282859097249

and

agent.Y_h = 1.0

1.0

Now, we will show how to add or remove agent instances from the model. Since agents are added by passing a NamedTuple of the fields we will use the fields of the agent we retrieved for ease of exposition

agentfields = Bit.getfields(agent)

(Y_h = 1.0, D_h = 3.7818066335944875, K_h = 6.973481059156251, w_h = 0.2697101055708983, O_h = 1, C_d_h = 0.0, I_d_h = 0.0, C_h = 0.0, I_h = 0.0)

Note

Importantly, fields can be accessed as long as the agent is still inside the model, and not after that. So, if you need those fields for something else after removing an agent, retrieve the fields before removing it.

delete!(model.w_act, id)
push!(model.w_act, agentfields);

We can also retrieve the id of the last agent added to the container with

id = Bit.lastid(model.w_act)

Let's finally verify that the last agent has Y_h equal to 1.0 as it should be

agent = model.w_act[id]
agent.Y_h

1.0