def _ndtr(x):
"""Implements ndtr core logic."""
dtype = lax.dtype(x).type
half_sqrt_2 = dtype(0.5) * np.sqrt(2., dtype=dtype)
w = x * half_sqrt_2
z = lax.abs(w)
y = lax.select(
lax.lt(z, half_sqrt_2),
dtype(1.) + lax.erf(w),
lax.select(lax.gt(w, dtype(0.)),
dtype(2.) - lax.erfc(z), lax.erfc(z)))
return dtype(0.5) * y
def erfc(x):
x, = _promote_args_inexact("erfc", x)
return lax.erfc(x)
