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the micro- and macro-level has to be ensured in any case. Both
approaches, bottom-up and top-down, may also be applied to the
development of the whole agent-based model.
It should be pointed out that the GRAMS reference model does not
imply the use of discrete time. At least within the conceptual model
a continuous time may be specified if suited for the model purpose.
Of course, a discretization of simulation time is usually unavoidable
in the course of the implementation as an executable software.
Example: Firespread
A discrete simulation time is chosen,
i.e.,
. For this example, a single time step represents an
interval of 1 minute.
T
=
N
6.4.2 Environment
In order to define actions of single agents and interactions between
multiple simulated agents, the common environment needs to be
defined. As an abstraction of the real environment, the
environment
E
denotes the common space in which all agents are acting. As for
the simulation time, restrictions imposed by the GRAMS reference
model are quite low: the simulated environment may be discrete or
continuous, bounded or unbounded and can be of arbitrary dimension
(although often 2-dimensional or 3-dimensional environments are used).
Except for environmental dynamics the environment is assumed to be
passive, but of course changeable.
Definition 12 (Environment)
The environment
E
=(
L
,
P
,
U
)is
defined as tuple of locations
L
, environmental properties
P
and envir-
U
onmental update functions
.
In order to embed entities into the environment at specific places,
the concept of
locations
is introduced. A location
l
∈
L
simply denotes
some connected space within the environment, with
denoting the
set of all possible locations. As the set of locations may change (e. g.,
due to an expanding world)
S
t
(
L
L
) denotes the set of locations at time
