The functions rotx, roty, rotz are not built-in of MATLAB (wtf). Instead
they come from a very expensive toolbox. As none other function of this
toolbox are needed, the functions are reimplemented manually for Rotare
to remove that useless dependency.

This completes the work started in !4 by implementing the true
Reynolds recalculation for the other three solvers.

Note that special care had to be implemented in Stahlhut solver in order
to ensure proper numerical resolution of the solution.

calculate reynolds number exact value in indvel.m
use its exact value when possible, if not use an approximation in ElemPerf.m