It is defined as: sigmoid(x) = 1 / (1 + exp(-x)).
For small values (<-5),
sigmoid returns a value close to zero, and for large values (>5)
the result of the function gets close to 1.
Sigmoid is equivalent to a 2-element softmax, where the second element is assumed to be zero. The sigmoid function always returns a value between 0 and 1.
See also
Other activations: activation_celu() activation_elu() activation_exponential() activation_gelu() activation_glu() activation_hard_shrink() activation_hard_sigmoid() activation_hard_tanh() activation_leaky_relu() activation_linear() activation_log_sigmoid() activation_log_softmax() activation_mish() activation_relu() activation_relu6() activation_selu() activation_silu() activation_soft_shrink() activation_softmax() activation_softplus() activation_softsign() activation_sparse_plus() activation_sparse_sigmoid() activation_sparsemax() activation_squareplus() activation_tanh() activation_tanh_shrink() activation_threshold()