sys.coords does not work as Vector{Vector}

[ejmeitz]

Just noticed that if you initialize the coordinates of your system with a Vector{Vector} instead of a Vector{SVector} you get an issue in the forces function specifically line 163 of forces.jl in the zero function. It probably pops up elsewhere also. The heart of the problem is for some reason:
zero([[1,2,3],[2,3,4]) is not valid but
zero([SVector(1,2,3), SVector(3,2,3)] is valid

Either we force the input to be a Vector of SVector or find a work around for the forces. I think that line is just trying to make a matrix the same shape as coords. similar might do the trick.

[jgreener64]

I think it's fair to assume that the coordinates are some array of SVectors or a similar bits type. There is a big performance hit otherwise.

[ejmeitz]

Makes sense. I'd like to add an error message about this though as the current error/crash is super unintuitive and I think its a pretty easy mistake to make. Will make a PR at some point.