discipline velocity
 potential Velocity;
enddiscipline

discipline position
 potential Position;
enddiscipline

module bouncing_ball();
 parameter real init_pos=10.0 from (0:inf),     // initial position of ball in
m
                g=9.81 from (0:inf),            // gravitational accelaration c
onst
                air_res=0.1 from (0:inf);       // air resistance
 velocity v;
 position p;

 integer mode;
`define revers 1
`define normal 0

 analog begin
   mode = `normal;
   // using the cross function to detect if Pos(p) has been fallen to zero
   // this will controll the time step, so that zero +- abstol is detected
   // accuracy of the resolution is controlled by the Position nature
   // accuracy can be tied by cross opt_args too

   @(cross(Pos(p),-1)) begin
        discontinuity(0);       // for velocity, 1st order for position
        mode = `revers;
   end

   if (Vel(v) > 0.0)
        af = -g - pow(Vel(v),2)*air_res;
   else
        af = -g + pow(Vel(v),2)*air_res;

   // use -Vel(v) at Pos(p) = 0
   Vel(v) <+ idt(af,-Vel(v),mode);

   // initial values for position are supplied as parameter and
   // used for initial value of the integral during dc analysis
   Pos(p) <+ idt(Vel(v),init_pos,analysis("static"));
 end
endmodule