[algorithm]——算法复杂度

$$
begin{align}
& phi(x,y) = phi left(sum_{i=1}^n x_iei, sum{j=1}^n y_jej right)
= sum{i=1}^n sum_{j=1}^n x_i y_j phi(e_i, e_j) =
& (x_1, ldots, x_n) left( begin{array}{ccc}
phi(e_1, e_1) & cdots & phi(e_1, e_n)
vdots & ddots & vdots
phi(e_n, e_1) & cdots & phi(e_n, e_n)
end{array} right)
left( begin{array}{c}
y_1
vdots
y_n
end{array} right)
end{align}
$$