- #1
camillio
- 74
- 2
Let C(X) be the set of continuous complex-valued bounded functions with domain X. Let {fn} be a sequence of functions on C. We say, that fn converges to f wrt to the metric of C(X) iff fn converges to f uniformly.
By definition of the uniform convergence, for any ε>0 there exists integer N s.t. n ≥ N implies |fn(x) - f(x)| ≤ ε for every x in X. Hence by the definition of supremum norm, the inequality is equivalent to sup(fn(x) - f(x)) ≤ ε.
I conclude, that:
1) the uniform convergence imposes that for every ε>0, there exists N from which on the functions fn and f are within this ε on whole X. Hence it always implies convergence wrt the metric of C(X), since exactly this ε can be used as the supremum of the distance fn and f.
2) What about the converse? I think, that if {fn} converges to f wrt to the metric of C(X), then the existence of such ε>0, being the supremum of the distance on whole X, implies the uniform convergence, as this ε can be used in its definition and the existence of N is guaranteed.
Am I right or not?
By definition of the uniform convergence, for any ε>0 there exists integer N s.t. n ≥ N implies |fn(x) - f(x)| ≤ ε for every x in X. Hence by the definition of supremum norm, the inequality is equivalent to sup(fn(x) - f(x)) ≤ ε.
I conclude, that:
1) the uniform convergence imposes that for every ε>0, there exists N from which on the functions fn and f are within this ε on whole X. Hence it always implies convergence wrt the metric of C(X), since exactly this ε can be used as the supremum of the distance fn and f.
2) What about the converse? I think, that if {fn} converges to f wrt to the metric of C(X), then the existence of such ε>0, being the supremum of the distance on whole X, implies the uniform convergence, as this ε can be used in its definition and the existence of N is guaranteed.
Am I right or not?