[hubertus65]

Modelica.Mechanics.MultiBody.Frames.smallRotation and Frames.TransformationMatrices.smallRotation return their result with an if-expression whose branches have different sizes. The condition is the function input withResidues:

output SI.Angle phi[if withResidues then 6 else 3];
algorithm
  phi := if withResidues then {T[2, 3], ..., T[1, 1]*T[2, 2] - T[2, 1]*T[1, 2] - 1} else {T[2, 3], -T[1, 3], T[1, 2]};

Branches of different array sizes require a parameter condition. OCT, the compiler of Modelon Impact, therefore rejects both functions:

If-expression with branches that have different array sizes must have parameter test-expression:
    {T[2,3], - T[1,3], T[1,2], T[1,1] - 1, T[2,2] - 1, T[1,1] * T[2,2] - T[2,1] * T[1,2] - 1} has size [6]
    {T[2,3], - T[1,3], T[1,2]} has size [3]

The declaration phi[if withResidues then 6 else 3] already fixes the size of phi. This PR assigns it in an if-statement instead:

  if withResidues then
    phi := {T[2, 3],-T[1, 3],T[1, 2],T[1, 1] - 1,T[2, 2] - 1,
      T[1, 1]*T[2, 2] - T[2, 1]*T[1, 2] - 1};
  else
    phi := {T[2, 3],-T[1, 3],T[1, 2]};
  end if;

Verification

The test model calls both functions with and without residues on a rotation axesRotations({1, 2, 3}, {a, 2*a, -a}) with a ramping to 1e-3.

Tool	Before	After
OpenModelica 1.27.1	simulates	bit-identical to before (20 variables)
OCT (Modelon Impact)	rejected (error above)	simulates, same values as OpenModelica

Nothing else in the MSL calls these functions; they are covered by a new ModelicaTest test on branch coverage-improvement.

🤖 Generated with Claude Code

https://claude.ai/code/session_01UmNZkRw6HV9CeBvNk36AzT