Hi,

Trying to simulate a model which worked perfectly using Dymola, I got the error:
Divide by zero
:

equation
  der(H3) = omega;
  der(H2) = Vx * Modelica.Math.sin(theta)+ X * Modelica.Math.cos(theta) * omega;
  der(H1) = Vx* Modelica.Math.cos(theta)+ X * Modelica.Math.sin(theta) * omega;
  Vx = Y * omega;
  Vy = - omega * X ;

  der(theta) = (-Vx) / X;
  der(X) = Modelica.Math.cos(theta) * Vx- Modelica.Math.sin(theta) * Vy;
  der(Y) = Modelica.Math.sin(theta) * Vx+ Modelica.Math.cos(theta) * Vy;
  (-Modelica.Math.sin(theta) * der(X)) + X * der(theta) = 0;