The first analytical expression to estimate photometric redshifts
  suggested by a machine
  We report the first analytical expression purely constructed by a machine to
determine photometric redshifts ($z_{\rm phot}$) of galaxies. A simple and
reliable functional form is derived using $41,214$ galaxies from the Sloan
Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method
automatically dropped the $u$ and $z$ bands, relying only on $g$, $r$ and $i$
for the final solution. Applying this expression to other $1,417,181$ SDSS-DR10
galaxies, with measured spectroscopic redshifts ($z_{\rm spec}$), we achieved a
mean $\langle (z_{\rm phot} - z_{\rm spec})/(1+z_{\rm spec})\rangle\lesssim
0.0086$ and a scatter $\sigma_{(z_{\rm phot} - z_{\rm spec})/(1+z_{\rm
spec})}\lesssim 0.045$ when averaged up to $z \lesssim 1.0$. The method was
also applied to the PHAT0 dataset, confirming the competitiveness of our
results when faced with other methods from the literature. This is the first
use of symbolic regression in cosmology, representing a leap forward in
astronomy-data-mining connection.
