Re: Lost on rigged Hilbert space



On Jun 2, 12:22 am, Martin Wanvik
<mart...@xxxxxxxxxxxx> wrote:
V' ~ (cl(V))' = H' ~ H (here ~ means "linearly
isometric"); H is
assumed to be real.
If V is dense and Hilbert then V = H.

The problem is when V is equipped with a finer
topology than H.
In this case, (V,<>_V) is a Hilbert space in its
own
right: it is
complete with respect to its own norm, but the
closure of V with
respect to the norm of H is H.

You are assuming a bit too much here, namely that
the topology on V comes from an inner product, or
even a single norm. Typically, it does not.

In this setting V could well be a proper subset
of
H...

Consider the case of Sobolev spaces H^m(R^n) (=:H^m),
with duals H^(-
m), (m integer for instance). They are Hilbert spaces
with the
following *continuous* injections :
H^m <= H^0 <= H^(-m)
I am concerned with the fact that we have these
inclusions on the one
hand, but H^(m) isomorphic to H^(-m) on the other
hand.

The spaces H^m are all separable (at least that is what Wikipedia tells me), and hence isomorphic to H^0 (or any other separable, infinite dimensional Hilbert space for that matter).
.



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