Interpolation classes and matrix monotone functions

Research output: Contribution to journalArticle


An interpolation function of order n is a positive function -/+ on (0, infinity) such that vertical bar vertical bar -/+ (A)(1/2) T -/+ (A)-(1/2) vertical bar vertical bar <= max(vertical bar vertical bar T vertical bar vertical bar, vertical bar A(1/2)TA(-1/2) vertical bar vertical bar) for all n x ii matrices T and A such that A is positive definite. By a theorem of Donoghue, the class C-n of interpolation functions of order n coincides with the class of functions -/+ such that for each n-subset S = {lambda i}(n)(i=1)of (0,infinity) there exists a positive Pick function h on (0, co) interpolating -/+ at S. This note comprises a study of the classes C-n and their relations to matrix monotone functions of finite order. We also consider interpolation functions on general unital C*-algebras.


  • Yacin Ameur
  • Sten Kaijser
  • Sergei Silvestrov
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Mathematics


  • interpolation function, matrix monotone function, Pick function
Original languageEnglish
Pages (from-to)409-427
JournalJournal of Operator Theory
Issue number2
Publication statusPublished - 2007
Publication categoryResearch