Let $H$ be a Hilbert space. Suppose we have $H_{n}\oplus G_{n}=H$ for all $% n\geq 0$ so that $\left( H_{n}\right) _{n\geq 0}$ is an increasing sequence of closed subspaces and $\left( G_{n}\right) _{n\geq 0}$ is a decreasing sequence of closed subspaces. I think we don't have in general : $H=% \overline{\underset{n\geq 0}{\bigcup }H_{n}}+\underset{n\geq 0}{\bigcap }% G_{n}$. My question is do we have : $H=\overline{\underset{n\geq 0}{\bigcup }H_{n}+\underset{n\geq 0}{\bigcap }G_{n}}$ ? This statement looks simple but seems to me hard to be confirmed or even disproved with a counter-example.
2026-03-28 00:28:55.1774657735
Infinite decomposition of a Hilbert space
60 Views Asked by Bumbble Comm https://math.techqa.club/user/bumbble-comm/detail AtRelated Questions in FUNCTIONAL-ANALYSIS
- On sufficient condition for pre-compactness "in measure"(i.e. in Young measure space)
- Why is necessary ask $F$ to be infinite in order to obtain: $ f(v)=0$ for all $ f\in V^* \implies v=0 $
- Prove or disprove the following inequality
- Unbounded linear operator, projection from graph not open
- $\| (I-T)^{-1}|_{\ker(I-T)^\perp} \| \geq 1$ for all compact operator $T$ in an infinite dimensional Hilbert space
- Elementary question on continuity and locally square integrability of a function
- Bijection between $\Delta(A)$ and $\mathrm{Max}(A)$
- Exercise 1.105 of Megginson's "An Introduction to Banach Space Theory"
- Reference request for a lemma on the expected value of Hermitian polynomials of Gaussian random variables.
- If $A$ generates the $C_0$-semigroup $\{T_t;t\ge0\}$, then $Au=f \Rightarrow u=-\int_0^\infty T_t f dt$?
Related Questions in HILBERT-SPACES
- $\| (I-T)^{-1}|_{\ker(I-T)^\perp} \| \geq 1$ for all compact operator $T$ in an infinite dimensional Hilbert space
- hyponormal operators
- a positive matrix of operators
- If $S=(S_1,S_2)$ hyponormal, why $S_1$ and $S_2$ are hyponormal?
- Is the cartesian product of two Hilbert spaces a Hilbert space?
- Show that $ Tf $ is continuous and measurable on a Hilbert space $H=L_2((0,\infty))$
- Kernel functions for vectors in discrete spaces
- The space $D(A^\infty)$
- Show that $Tf$ is well-defined and is continious
- construction of a sequence in a complex Hilbert space which fulfills some specific properties
Related Questions in PROJECTION
- What's wrong with my reasoning regarding projections
- Finding the orthogonal projection of a vector on a subspace spanned by non-orthogonal vectors.
- Coordinates of camera bounding box projected on another object.
- Bounded projection
- Deriving principal component out of cosine similarity
- Projection onto the space spanned by eigenfunctions in a Hilbert space
- Show that T - I is a projection.
- Pose estimation from 2 points and known z-axis.
- Non orthogonal projection of a point onto a plane
- Mercator projection - Use existing equation to solve for degrees
Related Questions in DIRECT-SUM
- Finding subspaces with trivial intersection
- Direct sum and the inclusion property
- direct sum of injective hull of two modules is equal to the injective hull of direct sum of those modules
- What does a direct sum of tensor products look like?
- does the direct sum of constant sequences and null sequences gives convergent sequence Vector space
- Existence of Subspace so direct sum gives the orignal vector space.
- A matrix has $n$ independent eigenvectors $\Rightarrow\Bbb R^n$ is the direct sum of the eigenspaces
- $\dim(\mathbb{V}_1 \oplus ...\oplus \mathbb{V}_k) = \dim\mathbb{V}_1+...+\dim\mathbb{V}_k$
- Product/coproduct properties: If $N_1\simeq N_2$ in some category, then $N_1\times N_3\simeq N_2\times N_3$?
- Direct Sums of Abelian Groups/$R$-Modules
Trending Questions
- Induction on the number of equations
- How to convince a math teacher of this simple and obvious fact?
- Find $E[XY|Y+Z=1 ]$
- Refuting the Anti-Cantor Cranks
- What are imaginary numbers?
- Determine the adjoint of $\tilde Q(x)$ for $\tilde Q(x)u:=(Qu)(x)$ where $Q:U→L^2(Ω,ℝ^d$ is a Hilbert-Schmidt operator and $U$ is a Hilbert space
- Why does this innovative method of subtraction from a third grader always work?
- How do we know that the number $1$ is not equal to the number $-1$?
- What are the Implications of having VΩ as a model for a theory?
- Defining a Galois Field based on primitive element versus polynomial?
- Can't find the relationship between two columns of numbers. Please Help
- Is computer science a branch of mathematics?
- Is there a bijection of $\mathbb{R}^n$ with itself such that the forward map is connected but the inverse is not?
- Identification of a quadrilateral as a trapezoid, rectangle, or square
- Generator of inertia group in function field extension
Popular # Hahtags
second-order-logic
numerical-methods
puzzle
logic
probability
number-theory
winding-number
real-analysis
integration
calculus
complex-analysis
sequences-and-series
proof-writing
set-theory
functions
homotopy-theory
elementary-number-theory
ordinary-differential-equations
circles
derivatives
game-theory
definite-integrals
elementary-set-theory
limits
multivariable-calculus
geometry
algebraic-number-theory
proof-verification
partial-derivative
algebra-precalculus
Popular Questions
- What is the integral of 1/x?
- How many squares actually ARE in this picture? Is this a trick question with no right answer?
- Is a matrix multiplied with its transpose something special?
- What is the difference between independent and mutually exclusive events?
- Visually stunning math concepts which are easy to explain
- taylor series of $\ln(1+x)$?
- How to tell if a set of vectors spans a space?
- Calculus question taking derivative to find horizontal tangent line
- How to determine if a function is one-to-one?
- Determine if vectors are linearly independent
- What does it mean to have a determinant equal to zero?
- Is this Batman equation for real?
- How to find perpendicular vector to another vector?
- How to find mean and median from histogram
- How many sides does a circle have?