OpenModelica 抱怨不能为负的负值

Question

遵循 this question I have modified the energy based controller which I have described here 以避免 sqrt 中出现负值：

model Model
  //constants
  parameter Real m = 1;
  parameter Real k = 2;
  parameter Real Fmax = 3;
  parameter Real x0 = 1;
  parameter Real x1 = 2;
  parameter Real t1 = 5;
  parameter Real v0 = -2;

  //variables
  Real x, v, a, xy, F, vm, K;

initial equation
  x = x0;
  v = v0;

equation
  v = der(x);
  a = der(v);
  m * a + k * x = F;

algorithm
  if time < t1 then
    xy := x0;
  else
    xy := x1;
  end if;
  
  K := Fmax * abs(xy - x) + k * (xy^2 - x^2) / 2;
  
  if abs(xy - x) < 1e-6 then
    F := k * x;
  else
    if K > 0 then
      vm := sign(xy - x) * sqrt(2 * K / m);
      F := Fmax * sign(vm - v);
    else
      F := Fmax * sign(x - xy);
    end if;
  end if;
  
  annotation(
    experiment(StartTime = 0, StopTime = 20, Tolerance = 1e-06, Interval = 0.001),
    __OpenModelica_simulationFlags(lv = "LOG_STATS", outputFormat = "mat", s = "euler"));
end Model;

但是，它一直给我错误：

The following assertion has been violated at time 7.170000

Model error: Argument of sqrt(K / m) was -1.77973e-005 should be >= 0

Integrator attempt to handle a problem with a called assert.

The following assertion has been violated at time 7.169500

Model error: Argument of sqrt(K / m) was -6.5459e-006 should be >= 0

model terminate | Simulation terminated by an assert at the time: 7.1695

STATISTICS

Simulation process failed. Exited with code -1.

如果您能帮助我了解问题所在以及如何解决，我将不胜感激。

Answer 1

您创建的代码执行事件本地化以查明 if 语句中的条件何时变为真 and/or 假。在此搜索过程中，平方根中的表达式可能会变为负数，尽管您使用 if 语句 'avoided' 它。

尝试阅读 this 并应用那里提供的解决方案。剧透：它基本上归结为为你的布尔条件添加一个 noEvent() 语句......

OpenModelica 抱怨不能为负的负值

OpenModelica complains about a negative value which can't be negative

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