  We present a numerical implementation of the infinite-range exterior complex
scaling (irECS) [Phys. Rev. A 81, 053845 (2010)] as an efficient absorbing
boundary to the time-dependent complete-active-space self-consistent field
(TD-CASSCF) method [Phys. Rev. A 94, 023405 (2016)] for multielectron atoms
subject to an intense laser pulse. We introduce Gauss-Laguerre-Radau quadrature
points to construct discrete variable representation basis functions in the
last radial finite element extending to infinity. This implementation is
applied to strong-field ionization and high-harmonic generation in He, Be, and
Ne atoms. It efficiently prevents unphysical reflection of photoelectron wave
packets at the simulation boundary, enabling accurate simulations with
substantially reduced computational cost, even under significant (~ 50%) double
ionization. For the case of a simulation of high-harmonic generation from Ne,
for example, 80% cost reduction is achieved, compared to a mask-function
absorption boundary.
