Weird behaviour with event detection

[casella]

Please consider the following test model

model Test
  Real a, b;
  discrete Real flag;
algorithm
  when a > 0 and b > 0 then
    flag := 1;
  end when;
initial algorithm
  if (a > 0) then
    flag := -1;
  end if;
equation
  a = 1+time;
  b = if time < (-1) then -1 else time;
annotation(experiment(StartTime=-2, StopTime=2));
end Test;

When simulating, the variable flag starts at -1, but only switches to +1 when time = 2, as if the event at time 0 was not caught.

Why does this happen?

[lochel]

No zero crossings are generated for the algorithm section.

[casella]

Replying to lochel:

No zero crossings are generated for the algorithm section.

Why not? Is this due to the language specification, or a missing implementation?

BTW, if I remove the condition a > 0 from the when statement, the event is triggered at time = 0 as expected

model Test
  Real a, b;
  discrete Real flag;
algorithm
  when b > 0 then
    flag := 1;
  end when;
initial algorithm
  if (a > 0) then
    flag := -1;
  end if;
equation
  a = 1+time;
  b = if time < (-1) then -1 else time;
annotation(experiment(StartTime=-2, StopTime=2));
end Test;

[casella]

Modelica 3.3r1, page 9

Algorithm sections where every section is treated as a set of equations which involves the variables occurring in the algorithm section

Modelica 3.3r1 page 92

The integration, is halted and an event occurs whenever a Real elementary relation, e.g. “ x > 2 ”, changes its value. The value of such a relation can only be changed at event instants [in other words, Real elementary relations induce state or time events].

As far as I understand, whether the when clause is contained in algorithm or equation section doesn't make any difference.

[casella]

Milestone changed to 1.13.0 since 1.12.0 was released

[casella]

Rescheduled to 1.14.0 after 1.13.0 releasee

[casella]

Releasing 1.14.0 which is stable and has many improvements w.r.t. 1.13.2. This issue is rescheduled to 1.16.0

[casella]

Retargeted to 1.17.0 after 1.16.0 release

[casella]

Retargeted to 1.18.0 because of 1.17.0 timed release.

[casella]

Ticket retargeted after milestone closed