OPT: maths: allows thr to be float
OPT: maths: allows thr to be float

Former-commit-id: 02824ddf298e74e8735ed7dbb047fa2d406a899e
Former-commit-id: fd51fe2a0c6c7d28377489da769e921c8a2311cb
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox