This is the class of visual inference quartic linear model, inherited from VI_MODEL.
See also
Parent class: VI_MODEL
New attributes: QUARTIC_MODEL$formula,
QUARTIC_MODEL$null_formula, QUARTIC_MODEL$alt_formula,
New methods: QUARTIC_MODEL$..init.., QUARTIC_MODEL$E,
QUARTIC_MODEL$sample_effect_size, QUARTIC_MODEL$set_prm