Unformatted text preview: Real Analysis  Math 630
Homework Set #10  Chapter 6
by Bobby Rohde 111700 Problem 7 a) For 1 p that v 1 v
v v p , we denote l p the space of all sequences v v 1 such . Prove the Minkowski ineqality for sequences
p v p v p. Here we have 1
v p p p
v1 ,
v p and v sup p Proof
Case 1
v p
p v1 v p
1 p v v p = v1 v v p 1 p . If either v or v has norm 0, the proof is trivial so we may assume that each has norm greater than v v 1, 1. 1 and then define real numbers , > 0 such that p p
v1 v1 v v p p
1 p v v1
v v p 1 p v p v1 1 p =
p v1
v v v p
v 1 p =
1 p p p , since p 1 and the quantities inside the distribution are each less than 1. , with 1. However expnading this expression and summing we see that it is in turn = 1 pp So v 1 v += v v p+ v p . QED. MATH63010.nb 2 Case p
v v v sup
v v p sup v v sup
1 p 1 q v + sup v = . QED.
v v b) Show that if
v1 v v l p and
p v v l q with
q 1, then Proof
Case p
v1 v 1, q
v v1 v sup v = v1 v v = v 1 v . Case 1 p
q Define v p . We may chosoe to assume that only on their absolute value. By Lemma 3 p t Summing
v v and
v v v are positive since the norm is dependant p p1 p =p t vt v v
v v1 p v both t
v pp sides.
v p p v1 pt
p t
v p v p p p v p = v t p
v v v p Differentiating with respect to t we have that v p v q . QED. v1 p p1 p = Problem 10 Let f n be a sequence of functions in L . Prove that f n converges to f in L if and only if there is a set E of measure 0 such that fn converges uniformly to f on E. Proof
fn f in L imples f n f except on a set E of measure 0, fn 0. Thus 0 N such that n N , f n f f . Thus fn is uniformly converges to f on E. . If fn uniformly converges to f except on a set E of measure 0 then and n N , fn x f x . except on E, f x < fn x bounded a.e. and hence f is in L . > 0, N such that x E ess sup fn x . Thus f is MATH63010.nb 3 Problem 11 Prove that L is complete. Proof
In order to show this we need that every Cauchy sequence of functions some f in L . Given > 0, N such that m, n N , f n fm norm we know that fn fm is bounded a.e. by . Define the pointwise limit f x It suffices to show that ess sup f limn fn in L converges to , by definition of Cauchy. Since this is L fn x , if the limit exists . , otherwise , since if fn converges then it must converge to f a.e. Since fn fm is bounded a.e. by , except on a set M of measure 0. However if we consider the collection of all such M m > n, we have a countable collection of sets of measure zero so there if limn fn x exists. Since fn is in L it union is also a set of measure 0. Thus fn x f x is bounded by some ess sup . Then where the limit exists, f is bounded by + . Thus we only need to show that the limit must exist upto a set of measure 0. MATH63010.nb 4 Problem 16 Let f n be a sequence of functions in L p, 1 p , which converge a.e. p . Show that to a function f in L f n converges to f in L p if and only if fn f. Proof
If fn fn fn
p
1 p fn f
p p f
1 p fn p f p 1 p fn 0, since p f 0 fn
p 1. However f p f , for p 1 fn f 0 fn f
p
1 p fn converges to f in L p f p. 0. However, fn f p ?????????????????????????????????? Demonstrate Proposition 8 fails at p = . Show that f , g functions , f L , such that step functions 0 and g and continuous 0. Counterexample on step functions.
Define f x sin 1 , x 0 x . 0, x 0 Clearly f x is bounded by 1 and thus in L . Consider a step function on partition 0 1 . Let denote the size of the smallest interval in the partition. 0 1 2 ... N Consider intervals of the form An = n1 , n 1 , for n . Clearly An 0, 1 , and infinitely 1 . Clearly by many An of length < . So choose n, m such that An m , m 1 and length An 1 construction f An 0, 1 , so regardless of the value of over m, m 1 , f 2 over An . 1 Hence f 2 . Thus showing the counter example to Proposition 8. MATH63010.nb 5 Counterexample on continuous functions.
Define g x 0, x 1, x
1 2 1 2 . approximating g. By continuity at x .
1 2 1 2 Clearly g is in L . Consider a continuous function 1 >0 > 0 such that x 1 ,x 2 2 Suppose that 1 0, then choose = 2 1 over this interval so g 2. Suppose that So g 8 at p =
1 2 1 2 , and the interval , 1 2 where x 1 2 , yet g = 1 . QED. 2 1 2 0, then choose . Thus g = 2 1 2 and the interval 1 2 , 1 2 where x 2 1 2 . > 0. Thus showing the counter example for Proposition ...
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This note was uploaded on 03/23/2010 for the course MATH 515 taught by Professor Staff during the Spring '08 term at Iowa State.
 Spring '08
 Staff
 Math

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