We use the continuous wavelet transform to generalize the multifractal formalism to fractal functions. We report the results of recent applications of the so-called wavelet transform modulus maxima (WTMM) method to fully developed turbulence data and DNA sequences. We conclude by brie y describing some works currently under progress, which are likely to be the guidelines for future research. c 1998 Elsevier Science B.V. All rights reserved
From global to local characterization of the regularity of fractal functionsIn many situations in physics as well as in some applied sciences, one is faced to the problem of characterizing very irregular functions [1][2][3][4][5][6][7][8][9][10][11]. The examples range from plots of various kinds of random walks, e.g. Brownian signals [12,13], to ÿnancial timeseries [14][15][16], to geological shapes [1,9,17], to medical time-series [18], to interfaces developing in far from equilibrium growth processes [4,6,11], to turbulent velocity signals [10,19,20] and to "DNA walks" coding nucleotide sequences [21,22]. These functions can be qualiÿed as fractal functions [1,13,[23][24][25] whenever their graphs are fractal sets in R 2 (for our purpose here we will only consider functions from R to R). They are commonly called self-a ne functions since their graphs are similar to themselves when transformed by anisotropic dilations, i.e., when shrinking along the x-axis by a factor followed by a rescaling of the increments of the function by a di erent factor −H