In: Advanced Math
definitions of weak topology and weak star topology with as little jargon as possible.
Let
be a non empty set and
be a family of topological spaces. Let
. Then we define weak topology
on
in such a way that
each
is continuous with respect to
in the following
way:
Since we expect each to be
continuous with respect to
, if
, then
. For
to be a topology,
it should be closed under arbitrary unions. Let
, then the topology generated by
is the required
topology, i.e.,
is the basis of the
weak topology
generated by
.
Let
be a normed space and
be its dual space.
For each
, the
functional
,
is a semi-norm on
. The topology
induced by the family of seminorms
is the weak topology on
. Thus, weak star
topology is nothing but the weak topology generated on the dual
space
by the family of
functions
which will
be continuous in this topology.
The aim to define this kind of topologies is to simplify our study of the space of continuous functions because every function on the topological space (with weak topology) is continuous.