This function models profiles of fast eye movements know as saccades based on a hyperbolic tangent function. The resulting saccades follow empirically measured and published main sequence functions. For more details see:
Mack, David J.; Belfanti, Sandro & Schwarz, Urs
"The effect of sampling rate and lowpass filters on saccades – A modeling approach"
Behavior Research Methods, 2017, DOI: 10.3758/s13428-016-0848-4
Updated the citation in the header. No functional changes