※ 引述《hometoofar (家太遠了)》之銘言：
: I am stuck on question 1 and 2 for homework 3 for a long time.
: Could someone give me a hint on them or point out if I am thinking in the
: right direction?
: For Q1, I try to expand the exponent in terms of xi1,xi2,xj1 and xj2 then I
: try to rearrange them so the expanded terms (other than the square of of the
: basic elements) fit well in the denomenator (n) of the infinite series
: e^n = (1+n/1!+n^2/2!+.......). No luck on this direction so far...
: I couldn't get something like what we have in the lecture.
Try to expand the term e^[-r<xi-xj,xi-xj>] and find out phi(x).
It's harder than that in the lecture ... but just need a trick.
: For Q2, suppose x is in n1 space and phi(x) is in n2 space; we need to
: express n2 in terms of n1 and maybe d (the exponent in poly kernel), right?
To decide the dimension of space of phi(x) in any proper a,b,d,and xE(R^n).