Models in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 386

10.2.3 Some related terminologies
10.2.3.1 Computer Model
Computer model is the numerical implementation of mathematical model, usu-
ally in the form of numerical discretization, solution algorithms, and convergence
criteria.
10.2.3.2 Simulation
Simulation reproduces the essence of a system without reproducing the system
itself. Mathematical simulation is a technique where by the behavior of a system is
described using a combination of mathematical and logical relationships. A system
is a part of reality that the engineers want to study.
10.2.3.3 Different Parameters and Variables in Modeling
Modeling : Modeling, especially scientific modeling, refers to the process of
generating a model as a conceptual representation of some phenomenon.
Model parameter : An item that is constant in the model; a number.
Variable : An item of interest that can change value depending on the other
components of the model.
State variable : A variable that describes the “status” of the system. There may
be more than one state variable in a model.
Rate variable : A rate variable is a quantity that defines some process within
the system at a given point in time. Rates always have dimensions of quan-
tity per unit time; they cannot be measured instantaneously similar to “state
variable.”
Control variable : A variable that is controllable by human, reflecting one or
more admissible policies. There may be more than one control variable in a
model.
Driving variable : Driving variable is the variable which initiates or drives the
main process of the system.
Constraint : Any condition that places bounds on the solution is a constraint.
Rate constant : Rate constant is the transfer rate of solute from one phase (e.g.,
solid, liquid, or gas) to another (in solute modeling).
Initial condition : Values of the state and control variables at the beginning of the
time period of interest. The behaviors of all dynamic system are dependent
upon their initial conditions. In classical mechanics, the initial conditions of
systems are known.
Boundary condition : Boundary conditions are the set of conditions specified for
the behavior of the solution to a set of differential equations at the bound-
ary of its domain. Boundary conditions are important in determining the
mathematical solutions to many physical problems.
Objective function : It is an equation that measures how well the system is
attaining an objective defined by the modeler. The objective function is