Exercise 1: Feature Map Let
x,yinR^(2)
, i.e.
x=(x_(1),x_(2))
and
y=(y_(1),y_(2))
. Define polynomial kernel
K:R^(2)\times R^(2)->R
by
K(x,y)=(x^(TT)y)^(2)
. Find the feature map
\phi :R^(2)->R^(D)
. Please specify the dimension
D
. Consider the same kernel function
K(x,y)=(x^(TT)y)^(2)
which is defined on
R^(3)\times R^(3)
in this part, i.e.
x,yinR^(3)
. What is the feature map
\phi :R^(3)->R^(D)
? What is the dimension
D
? In general, suppose that
x,yinR^(d)
and polynomial kernel is defined as
K(x,y)=(x^(TT)y)^(2)
. Without writing the feature map
\phi :R^(d)->R^(D)
explicitly, write down the dimension
D
as a function of input dimension
d
.