Lecture 0
Course overview
In this course, we will mainly be concerned with the following problems:
1) Harmonic functions u = 0, i.e. i uii = 0.
Dirichlet problem: ( Rn )
u = 0 , x ,
u=
, x .
2) Heat e
Lecture 1
Mean Value Theorem
Theorem 1 Suppose Rn , u C 2 (), u = 0 in , and B = B (y, R) , then
1
1
u(y ) =
uds =
udx
nn Rn1 B
n R n B
Proof:By Greens formula, for r (0, R),
0=
Br
=
1
r n1
Br
u
ds
Lecture 2
Denition of Greens function for general domains.
Suppose u C 2 () C 1 (), then for y , the Green Representation formula tells
us
u
u(y ) =
(u (x y ) (x y ) )d +
(x y )udx.
Denition 1 For int
Lecture 3
MVP + integrable harmonic
Theorem 1 Suppose u L1oc , then u is harmonic u satises MVP on .
l
Proof: Take C function on Rn with p
roperties: (a) S upp() B (0, 1); (b) 0;
(c) is radical, i.e.
Lecture 4
Removable Singularity Theorem
Theorem 1 Let u be harmonic in \ cfw_x0 , if
o(|x x0 |2n )
u(x) =
o(ln |x x0 |)
,
,
n > 2,
n=2
as x x0 , then u extends to a harmonic function in .
Proof: Witho