Skip to contents

Log-sigmoid (numerically stable)

Source: R/stability.R
log_sigmoid.Rd

Computes log(sigmoid(x)) = -log(1 + exp(-x)) stably.

Usage

log_sigmoid(x)

Arguments

x

A value object or numeric

Value

log(sigmoid(x))

Details

Direct computation of log(sigmoid(x)) fails for large negative x (sigmoid underflows to 0). This uses:

  • For x >= 0: -log(1 + exp(-x)) = -softplus(-x)

  • For x < 0: x - log(1 + exp(x)) = x - softplus(x)