Help System (web edition)

Functions available in ESTIMATE model specifications:

Functions with derivatives:
sqrt, log (ln), exp, sin, cos, tan, atan (arctan), sinh, cosh,
tanh, asin (arcsin), acos (arccos), lgamma, phi, PHI.

lgamma is the logarithm of the gamma function.
phi and PHI are the density and cumulative distiribution functions
of the standardized normal distribution, respectively.

Functions without derivatives:
abs, int, round.

round(x) is x rounded to the nearest integer.
  S = more on extra specifications in ESTIMATE