same question in stackoverflow

I'm trying to create a model where one Modelica variable is a triangular wave of another variable. First I tried the floor() function as below:

model test1

  final constant Real pi=2*Modelica.Math.asin(1.0);

  parameter Real b = 1;

  parameter Real a = 1;

  Real x,p,u;

equation

  if sign(sin(x*pi/b))>=0 then 

    p=a*(x-b*floor(x/b));

  else 

    p=a*(b-(x-b*floor(x/b)));

  end if;

  x=time;

  u = floor(x/b);

end test1

(x=time; is arbitrary so the model compiles)

but the result is weird, as you can see below


zoom in:



somehow 0.005 seconds before the next step floor function behaves unexpectedly and becomes a linear function ending by the next value.



then I tried the ceil() function. everything seemed right till I realised the same problem happens with ceil() function at other values (e.g. x=13)

I would appreciate if you could:

1. help me understand why this "glitch" happens and if it is intentional by design or a bug?

2. how I can fix this?

3. are there any alternatives to create a triangular wave function?

P.S. I am using this "wave function" to model the interaction between two jagged bodies