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The dynamic behaviour of a model is described by changes of variables of state within differential equations and events.

On grounds of various facts it is useful or necessary to calculate intermediate values of quantities:
  • to pass a model quantity to another component
  • to display physically relevant variables in an intermediate point in time
  • to get clear formulations and presentations
  • to deduct further interesting quantities from the results
  • to represent implicit correlations iteratively.


Such intermediate or derived quantities are represented by algebraic equations.

Algebraic equations define a variable either by an algebraic expression or by one or more case distinctions .
Pendulum
Example: Pendulum

DIFFERENTIAL EQUATIONS
phi'  := vPhi;
vPhi' := aPhi;
END

a    := g*SIN(phi);
aPhi := a/l;

x := l*SIN(phi);
y := l*COS(phi);

The acceleration a and the angular acceleration aPhi are defined by algebraic equations before they are plugged into the differential equation.

The location in carthesian coordinates is derived from the representation in polar coordinates.