In: Advanced Math
For each n ∈ N, let fn : [0, 1] → [0, 1] be defined by fn(x) = 0, x > 1/n and fn(x) = 1−nx if 0 ≤ x ≤1/n.
The collection {fn(x) : n ∈ N} converges to a point,
call it f(x) for each x ∈ [0, 1]. Show whether {fn(x) :
n ∈ N}
converges to f uniformly or not.
for all n. For
by Archimedean property real numbers, there exist
(a fixed natural number) such that
. So for all
. Hence, for all
,
and
(by definition). This is because for
,
after finitely many non-zero
all other
. So,
and
as at
, it is the constant sequence 1and for
, after finitely many non-zero terms, the sequence is eventually
constant sequence 0.
Claim:
does not converges to
uniformly.
where supremum runs over
. Since, 1 does not tends to zero. Hence, we are done.
Also, there is a theorem that if sequence of continuous
functions converges uniformly then the limit function is
continuous. Here,
are continuous throughout and f(x) is not continuous at x=0. So,
they cannot converge uniformly.