You want to minimize a differentiable real-valued function fon a smooth hypersurface S. If such a minimum exists - in the situation after editing it is guaranteed to exist, because the hypersurface is compact - it occurs at the critical point of the restriction f|Sfrom fto S.
f, , M, - , gradient of f T(M) . .
, ( 1), () g(x) = 0 g, , f|S - x S, grad(f)|x grad(g)|x.
( ), ( ).
,
S, , (x|x) = 1, (a|b) a_1*b_1 + ... + a_k*b_k, g at x 2*xL(x) = (c|x) = c_1*x_1 + ... + c_k*x_k, L x
, L ( c = 0, L ), , c , c/|c| -c/|c|.
, L(c/|c|) = 1/|c|*(c|c) = |c| L(-c/|c|) = -1/|c|*(c|c) = -|c|, -c/|c|, -|c|.