Compatibility issue with MATLAB R2025b: "Colon operands must be real scalars" in PCRegionGrowing.m

[PatrikMrnka]

Hi Luca,
I'm testing STAPLE with the latest MATLAB R2025b and OpenSim 4.1. I encountered a runtime error during the femoral condyle extraction phase.

Error log:

Error using :
Colon operands must be real scalars.
Error in PCRegionGrowing (line 28)
Pts_Out(end+1:end+size(idx),:) =  Pts(idx,:);

Cause:
In newer MATLAB versions (R2023a+), the colon operator strictly requires scalars. size(idx) returns a 1x2 vector (e.g., [N, 1]), which triggers this error.

Suggested Fix:
Changing size(idx) to length(idx) or size(idx, 1) on line 28 of PCRegionGrowing.m resolves the issue:
Pts_Out(end+1:end+length(idx),:) = Pts(idx,:);

Verified: replacing size() with length() fixes the crash and allows the model generation to continue.