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9 - The ⋆-Function

Published online by Cambridge University Press:  22 February 2019

Albert Baernstein II
Affiliation:
Washington University, St Louis
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Summary

This chapter marks the debut of the star function in the book. Each type of rearrangement has an associated star function, which is an indefinite integral of the rearranged function. This chapter proves ``subharmonicity'' theorems for the star function, expressing the fact that if a function satisfies a Poisson-type partial differential equation then its star function satisfies a related differential inequality. In the simplest case of circular symmetrization in the plane, the result says that if a function is subharmonic then so is its star function. Subharmonicity is applied in the succeeding chapters to yield comparison theorems for solutions of partial differential equations and extremal results in complex analysis.

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Publisher: Cambridge University Press
Print publication year: 2019

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  • The ⋆-Function
  • Albert Baernstein II, Washington University, St Louis
  • Book: Symmetrization in Analysis
  • Online publication: 22 February 2019
  • Chapter DOI: https://doi.org/10.1017/9781139020244.012
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  • The ⋆-Function
  • Albert Baernstein II, Washington University, St Louis
  • Book: Symmetrization in Analysis
  • Online publication: 22 February 2019
  • Chapter DOI: https://doi.org/10.1017/9781139020244.012
Available formats
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Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • The ⋆-Function
  • Albert Baernstein II, Washington University, St Louis
  • Book: Symmetrization in Analysis
  • Online publication: 22 February 2019
  • Chapter DOI: https://doi.org/10.1017/9781139020244.012
Available formats
×