I am trying to develop my own package, which contains fuctions that helps kinematic calculations. One of these fucntion:

My problem is, that in my notebook, the function works properly only if I evaluated the cell in my package where the function is (with shift+enter). Before that, I always get a null matrix which means my notebook sees the function, but I think the local variables in the Module function (a,b,c) are not evaluated. I tried with Evaluate function but this did not work either. I found the following in the Mathematica documentation: I think this can be related somehow to my problem, but i am not sure and i do not really understand what is the difference between Function[x,e] and Function@@{x,e}. To sum up: After shift enter in the package, the function works properly in notebook, before shift enter, it works incorrectly. Why is that. Thank you and sorry for my bad english.