a = 0 (slider from -5 to 5, step 0.1)
b = 1 (slider from -5 to 5, step 0.1)
u = Vector((0, 0), (a, b))
z: (a, b)
O = (0, 0)
T1: "z=" + (LaTeX[a]) + "+" + (LaTeX[b]) + "i"