X = {x}
Y = {y}
d
n
(x, y)
X
n
×Y
n
= {(x, y), x ∈ X
n
, y ∈ Y
n
}
• x = (x
1
, ..., x
n
) y = (y
1
, ..., y
n
)
d
n
(x, y) =
1
n
n
X
i=1
d(x
i
, y
i
),
d(x, y)
•
d(x, y) ≥ 0 x ∈ X, y ∈ Y.
d(x, y)
x y
X = {0, ..., M − 1} Y = X
d(x, y) =
½
0, x = y;
1, x 6= y.
y x
d
n
(x, y)