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Everything about Functional calculus

Theory allowing one to apply mathematical functions to mathematical operators

In mathematics, a functional calculus is a theory allowing one to apply mathematical functions to mathematical operators. It is now a branch of the field of functional analysis, connected with spectral theory. Historically, the term was synonymous with the calculus of variations; the latter term remains in extensive use in physics and engineering texts, whereas functional calculus develops the subject further with more mathematically careful, formal, abstract and precise articulations. The older usage is still visible in the functional derivative, which is often called the variational derivative. Wikipedia →

🧭 Start here: a 6-step reading path

  1. Read the overview: Functional calculusA 5-minute orientation
  2. Skim a recent paper: Axially Harmonic Functions and the Harmonic Functional Calculus on the S-spectrumInfluential work since 2022
  3. Pick up a classic book: A Course of Pure MathematicsThe most-reprinted book on the subject
  4. Read the landmark paper: Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force FieldsCited 22,851 times
  5. Go sideways: Borel functional calculusA closely related topic
  6. Go sideways: Composition operatorA closely related topic

📖 Definitions

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🗂️ The subject at a glance

  1. Usage
  2. Informal motivation

🏆 Landmark papers (most cited)

🆕 Influential since 2022

📚 Books worth reading

Ranked by number of editions on Open Library, a rough measure of how lasting a book is.

🔗 Related topics