  MAx is a new tool to estimate parameters from stellar spectra. It is based on
the maximum likelihood method, with the likelihood compressed in a way that the
information stored in the spectral fluxes is conserved. The compressed data are
given by the size of the number of parameters, rather than by the number of
flux points. The optimum speed-up reached by the compression is the ratio of
the data set to the number of parameters. The method has been tested on a
sample of low-resolution spectra from the Sloan Extension for Galactic
Understanding and Exploration (SEGUE) survey for the estimate of metallicity,
effective temperature and surface gravity, with accuracies of 0.24 dex, 130K
and 0.5 dex, respectively. Our stellar parameters and those recovered by the
SEGUE Stellar Parameter Pipeline agree reasonably well. A small sample of
high-resolution VLT-UVES spectra were also used to test the method and the
results have been compared to a more classical approach. The speed and
multi-resolution capability of MAx combined with its performance compared with
other methods indicates that it will be a useful tool for the analysis of
upcoming spectral surveys.
