Skip to content Skip to navigation

Connexions

You are here: Home » Content » Plancharel and Parseval's Theorems

Navigation

Lenses

What is a lens?

Definition of a lens

Lenses

A lens is a custom view of Connexions content. You can think of it as a fancy kind of list that will let you see Connexions through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to Connexions materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual Connexions member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

This content is ...

Affiliated with (What does "Affiliated with" mean?)

This content is either by members of the organizations listed or about topics related to the organizations listed. Click each link to see a list of all content affiliated with the organization.
  • OrangeGrove display tagshide tags

    This module is included inLens: Florida Orange Grove Textbooks
    By: Florida Orange GroveAs a part of collection:"Signals and Systems"

    Click the "OrangeGrove" link to see all content affiliated with them.

    Click the tag icon tag icon to display tags associated with this content.

Also in these lenses

  • richb's DSP display tagshide tags

    This module is included inLens: richb's DSP resources
    By: Richard BaraniukAs a part of collection:"Signals and Systems"

    Comments:

    "My introduction to signal processing course at Rice University."

    Click the "richb's DSP" link to see all content selected in this lens.

    Click the tag icon tag icon to display tags associated with this content.

Recently Viewed

This feature requires Javascript to be enabled.

Tags

(What is a tag?)

These tags come from the endorsement, affiliation, and other lenses that include this content.

Plancharel and Parseval's Theorems

Module by: Justin Romberg. E-mail the author

User rating (How does the rating system work?)
Ratings

Ratings allow you to judge the quality of modules. If other users have ranked the module then its average rating is displayed below. Ratings are calculated on a scale from one star (Poor) to five stars (Excellent).

How to rate a module

Hover over the star that corresponds to the rating you wish to assign. Click on the star to add your rating. Your rating should be based on the quality of the content. You must have an account and be logged in to rate content.

:
(0 ratings)

Summary: This module contains the definition of the Plancharel theorem and Parseval's theorem along with proofs and examples.

Note: Your browser may not currently support MathML. See our browser support page for additional details. You can always view the correct math in the PDF version.

Plancharel Theorem

Theorem 1: Plancharel Theorem

The inner product of two vectors/signals is the same as the ℓ2 ℓ 2 inner product of their expansion coefficients.

Let b i b i be an orthonormal basis for a Hilbert Space H H. x∈H x H , y∈H y H x=∑ α i b i x i α i b i y=∑ β i b i y i β i b i then <x,y> H =∑ α i β i ¯ x y H i α i β i

Example

Applying the Fourier Series, we can go from ft f t to c n c n and gt g t to d n d n ∫0Tftgt¯dt=∑n=-∞∞ c n d n ¯ t 0 T f t g t n c n d n inner product in time-domain = inner product of Fourier coefficients.

Proof

x=∑ α i b i x i α i b i y=∑ β j b j y j β j b j <x,y> H =<∑ α i b i ,∑ β j b j >=∑ α i < b i ,∑ β j b j >=∑ α i ∑ β j ¯< b i , b j >=∑ α i β i ¯ x y H i α i b i j β j b j i α i b i j β j b j i α i j β j b i b j i α i β i by using inner product rules

Note:
< b i , b j >=0 b i b j 0 when i≠j i j and < b i , b j >=1 b i b j 1 when i=j i j

If Hilbert space H has a ONB, then inner products are equivalent to inner products in ℓ2 ℓ 2 .

All H with ONB are somehow equivalent to ℓ2 ℓ 2 .

Point of interest:
square-summable sequences are important

Parseval's Theorem

Theorem 2: Parseval's Theorem

Energy of a signal = sum of squares of it's expansion coefficients

Let x∈H x H , b i b i ONB

x=∑ α i b i x i α i b i Then ∥x∥H2=∑| α i |2 H x 2 i α i 2

Proof

Directly from Plancharel ∥x∥H2= <x,x> H =∑ α i α i ¯=∑| α i |2 H x 2 x x H i α i α i i α i 2

Example 1

Fourier Series 1Tⅇⅈ w 0 nt 1 T w 0 n t ft=1T∑ c n 1Tⅇⅈ w 0 nt f t 1 T n c n 1 T w 0 n t ∫0T|ft|2dt=∑n=-∞∞| c n |2 t 0 T f t 2 n c n 2

Download LabVIEW Source

Content actions

Give Feedback:

E-mail the module author | Rate module ( How does the rating system work?)

Rating system

Ratings

Ratings allow you to judge the quality of modules. If other users have ranked the module then its average rating is displayed below. Ratings are calculated on a scale from one star (Poor) to five stars (Excellent).

How to rate a module

Hover over the star that corresponds to the rating you wish to assign. Click on the star to add your rating. Your rating should be based on the quality of the content. You must have an account and be logged in to rate content.

(0 ratings)

Download:

Module PDF

Add module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections directly in Connexions. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need a Connexions account to use 'My Favorites'.

| A lens (?)

Definition of a lens

Lenses

A lens is a custom view of Connexions content. You can think of it as a fancy kind of list that will let you see Connexions through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to Connexions materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual Connexions member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks