Diagnostic equation
Encyclopedia
In a physical simulation context, a diagnostic equation (or diagnostic model) is an equation (or model) that links the values of these variables simultaneously, either because the equation (or model) is time-independent, or because the variables all refer to the values they have at the same identical time. This is by opposition to a prognostic equation
.
For instance, the so-called ideal gas law
(PV = nRT) of classical thermodynamics
relates the state variable
s of that gas, all estimated at the same time. It is understood that the values of any one of these variables can change in time, but the relation between these variables will remain valid at each and every particular instant, which implies that one variable cannot change its value without the value of another variable also being affected.
Prognostic equation
Prognostic equation - in the context of physical simulation, a prognostic equation predicts the value of variables for some time in the future on the basis of the values at the current or previous times....
.
For instance, the so-called ideal gas law
Ideal gas law
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...
(PV = nRT) of classical thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
relates the state variable
State variable
A state variable is one of the set of variables that describe the "state" of a dynamical system. Intuitively, the state of a system describes enough about the system to determine its future behaviour...
s of that gas, all estimated at the same time. It is understood that the values of any one of these variables can change in time, but the relation between these variables will remain valid at each and every particular instant, which implies that one variable cannot change its value without the value of another variable also being affected.