[LONGITUDINAL]  
input = {a}

EQUATION:
t0 = 0
f_0 = 0
ddt_f = a

;--------------------------------------------
[INDIVIDUAL]  ; variability levels = {id, occ}
input = {a_pop, oa0, oa1}

DEFINITION:
a = {distribution=normal, reference=a_pop, varlevel={id,id*occ}, sd= {oa0, oa1}}
