It is well-known that
the best Diophantine approximations to a single real number 𝜃 are exactly
the convergents of the continued fraction expansion of 𝜃. The properties of
one-dimensional best approximations that make this true are shown not to hold
in general for best simultaneous Diophantine approximations to α ∈Rn
when n ≧ 2. They do hold in a weak form for all badly approximate vectors
α ∈ Rn.