LOG1P

Purpose:

Computes log(1 + x) for small x.

LOG1P(x)

A scalar, series or table.

A scalar, series, or table.

log1p(1e-17)

returns 1.000000E-17.

log(1 + 1e-17)

returns 0.0.

expm1(log1p(1e-17))

returns 1.000000E-17.

exp(log(1 + 1e-17)) - 1

returns 0.0.

For real values, LOG1P is accurate for small x where 1 + x == 1 for double precision accuracy.

For small x, LOG1P(x) is approximately x, but LOG(1 + x) is approximately 0 for double precision accuracy.

See EXPM1 to compute EXP(x) - 1 for small x, the inverse of LOG1P.