Mock data sets for Lyman-alpha forest surveys

We present a set of publicly available codes to generate mock Lyman-$\alpha$ (\lya) forest data sets. The codes are based on 
the Fluctuating Gunn-Petterson Approximation  (FGPA) applied to
Gaussian random fields and on the use of fast Fourier transforms (FFT). The output includes spectra of \lya\ transmitted-flux-fraction, $F$, a quasar catalog, and a catalog of high-column-density systems. Additional codes are then required to generate 
realistic unabsorbed quasar spectra and to add absorption by high-column-density systems  and metals and instrumental effects. 
Redshift space distortions (RSD) are implemented by including the  large-scale velocity-gradient field in the FGPA
resulting in a  the correlation function of $F$ that can be accurately predicted.  
One hundred realizations have been produced over the 14,000 deg${}^2$ DESI survey footprint with 100 quasars per deg${}^2$, and they are currently being used for the eBOSS and DESI surveys.
The analysis of these realizations shows that the correlation of $F$ follows the prediction within the accuracy of eBOSS survey.
The most time-consuming part of the production occurs before application of the FGPA.
We  therefore save pre-FGPA forests which allows us to easily produce new mock sets with modified redshift-dependent bias parameters and instrumental effects.