10
1 Modeling Systems
Fig. 1.3 Free fall of the
body from a given height
As known, it is described by:
d
2 h
dh 2 = −g.
h(0) = h 0 ;
dh
dt
t=0
= v 0 ,
The parameter g outwardly does not differ in any way from h 0 and v 0 , but it
is not a characteristic of the object, but of the medium in which it is located, i.e.,
characterizes the planet on which the experiment is conducted. This means that in
reality the object is not isolated, but at the same time, an object model that takes into
account the properties of the medium is considered to be isolated.
At the same time, there are cases when it is convenient to consider the object and
the environment separately. Then, the model consists of two parts (components): the
object model itself and the environment model. The interaction between them occurs
through external variables for some specific laws. In this case, they say that the actual
model of the object will be open.
Isolated single-component (that is, without internal structure) models are the simplest type of models. All variables of such models are logically divided into state
variables, parameters, and constants. The difference between a parameter and a constant is that the constant is set at the stage of building the model and cannot be changed
during a computational experiment, whereas the parameters cannot be changed during a separate experiment but can be changed during a series of experiments. It can
be said otherwise that the parameters serve to “tune” the properties of the object
being modeled.