Use expm1 in elu
expm1(x) is more accurate than exp(x) - 1 when x is nearly, but not
exactly, zero.
In the case of elu, we would compute exp(x) - 1 when x is <= 0. If x is
negative and has a very small magnitude, computing exp(x) - 1 would
round to zero.
For example, if x was -1.0E-8 then:
exp(x) - 1 is 0 but expm1(x) is -1.0E-8
