This is the standard identity to derive nax from nqx and nMx.
lt_id_qm_a(nqx, nMx, AgeInt)
numeric. Vector of age specific death probabilities.
numeric. Vector of age-specific death rates.
integer. Vector of age class widths.
nax numeric vector of average time spent in interval by those dying in interval via identity.
Preston S, Heuveline P, Guillot M (2000). Demography: measuring and modeling population processes. Wiley-Blackwell.