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How is the LpL^p function space defined via the p-norm?

The LpL^p space is defined as the set of all measurable functions whose p-norm is strictly less than positive infinity.

Conditions

  • The p-norm ∥f∥p\|f\|_p has been defined.
  • f is a measurable function.

Reasoning, step by step

  1. Define the p-norm ∥f∥p\|f\|_p for a measurable function.
  2. Evaluate the p-norm for various measurable functions.
  3. Collect all measurable functions for which the calculated p-norm is finite (less than +∞+\infty).
  4. Formally denote this collection as the LpL^p space.

Example

The video writes the set-builder notation on the board: Lp:={f measurable:∥f∥p<+∞}L^p := \{ f \text{ measurable} : \|f\|_p < +\infty \}.

Common misconceptions

  • Assuming LpL^p is inherently a Banach space from the start; the video notes it is initially just a set, and its linear space and completeness structures must be verified step by step later.
  • Confusing the space LpL^p with the norm ∥f∥p\|f\|_p; the norm is a value, while the space is the collection of functions for which that value is finite.

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Answers are generated from source material and independently checked. Consult the original video or creator if something is unclear.