The ensemble photometric variability of over $10^5$ quasars in the Dark
  Energy Camera Legacy Survey and the Sloan Digital Sky Survey
  We present the ensemble variability analysis results of quasars using the
Dark Energy Camera Legacy Survey (DECaLS) and the Sloan Digital Sky Survey
(SDSS) quasar catalogs. Our dataset includes 119,305 quasars with redshifts up
to 4.89. Combining the two datasets provides a 15-year baseline and permits
analysis of the long timescale variability. Adopting a power-law form for the
variability structure function, $V=A(t/1yr)^{\gamma}$, we use the
multi-dimensional parametric fitting to explore the relationships between the
quasar variability amplitude and a wide variety of quasar properties, including
redshift (positive), bolometric luminosity (negative), rest-frame wavelength
(negative), and black hole mass (uncertain). We also find that $\gamma$ can be
also expressed as a function of redshift (negative), bolometric luminosity
(positive), rest-frame wavelength (positive), and black hole mass (positive).
Tests of the fitting significance with the bootstrap method show that, even
with such a large quasar sample, some correlations are marginally significant.
The typical value of $\gamma$ for the entire dataset is $\gtrsim 0.25$,
consistent with the results in previous studies on both the quasar ensemble
variability and the structure function. A significantly negative correlation
between the variability amplitude and the Eddington ratio is found, which may
be explained as an effect of accretion disk instability.
