Let be a Borel probability measure on R . We study the Hausdorff dimension and the packing dimension of the multifractal Hausdorff measurehq;t and the multifractal packing measure p q;t introduced in [L. Olsen, A multifractal formalism, Advances in Mathematics 116 (1995), 82^196]. Let b denote the multifractal Hausdorff dimension function and let B denote the multifractal packing dimension function introduced in [Olsen, op_ cit_]. For a fixed q 2 R, we obtain bounds for the Hausdorff dimension and the packing dimension of hq;b q and p q;B q in terms of the subdifferential of b and B at q. For q 1, our result reduces to yDB 1 lim inf r&0 log B x; r log r lim sup r&0 log B x; r log r yDyB 1 for -a.a. x where DyB 1 and DB 1 denote the left and right derivative of B at 1. Inequality ( ) improves a similar result obtained independently by Y: Heurteaux and S:-Z: Ngai. It follows from ( ) that if the mulifractal box dimension spectrum (or Lq spectrum) of is differentiable at 1 then y 0 1 equals the entropy dimension (or information dimension) of . This result has been conjectured in the physics literature and proved rigorously in certain special cases.
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