# BNNS.ActivationFunction Constants that describe activation functions. ``` enum ActivationFunction ``` ## Topics ### Activation Functions [`case abs`](/documentation/Accelerate/BNNS/ActivationFunction/abs) An activation function that returns the absolute value of its input. [`case celu(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/celu(alpha:)) An activation function that evaluates the continuously differentiable exponential linear units (CELU) on its input. [`case clamp(bounds: ClosedRange)`](/documentation/Accelerate/BNNS/ActivationFunction/clamp(bounds:)) An activation function that returns its input clamped to the specified range. [`case clampedLeakyRectifiedLinear(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/clampedLeakyRectifiedLinear(alpha:beta:)) An activation function that returns its input clamped to beta when that is greater than or equal to zero, otherwise it returns its input multiplied by alpha clamped to beta. [`case elu(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/elu(alpha:)) An activation function that evaluates the exponential linear units (ELU) on its input. [`case geluApproximation(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/geluApproximation(alpha:beta:)) An activation function that evaluates the Gaussian error linear units (GELU) approximation on its input. [`case geluApproximation2(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/geluApproximation2(alpha:beta:)) An activation function that provides a fast evaluation of the Gaussian error linear units (GELU) approximation on its input. [`case gumbel(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/gumbel(alpha:beta:)) An activation function that returns random numbers from the Gumbel distribution. [`case gumbelMax(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/gumbelMax(alpha:beta:)) An activation function that returns random numbers from the Gumbel distribution. [`case hardShrink(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/hardShrink(alpha:)) An activation function that returns zero when the absolute input is less than alpha, otherwise it returns its input. [`case hardSigmoid(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/hardSigmoid(alpha:beta:)) An activation function that returns the hard sigmoid function of its input. [`case hardSwish(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/hardSwish(alpha:beta:)) An activation function that returns the hard swish function of its input. [`case identity`](/documentation/Accelerate/BNNS/ActivationFunction/identity) An activation function that returns its input. [`case leakyRectifiedLinear(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/leakyRectifiedLinear(alpha:)) An activation function that returns its input when that is greater than or equal to zero, otherwise it returns its input multiplied by a specified value. [`case linear(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/linear(alpha:)) An activation function that returns its input multiplied by a specified value. [`case linearWithBias(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/linearWithBias(alpha:beta:)) An activation function that returns its input multiplied by a scale and added to a bias. [`case logSigmoid`](/documentation/Accelerate/BNNS/ActivationFunction/logSigmoid) An activation function that returns the logarithm of the sigmoid function of its input. [`case logSoftmax`](/documentation/Accelerate/BNNS/ActivationFunction/logSoftmax) An activation function that returns the logarithm of the softmax function of its input. [`case rectifiedLinear`](/documentation/Accelerate/BNNS/ActivationFunction/rectifiedLinear) An activation function that returns its input when that is greater than or equal to zero, otherwise it returns zero. [`case scaledTanh(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/scaledTanh(alpha:beta:)) An activation function that returns the scaled hyperbolic tangent of its input. [`case selu`](/documentation/Accelerate/BNNS/ActivationFunction/selu) An activation function that evaluates the scaled exponential linear units (SELU) on its input. [`case sigmoid`](/documentation/Accelerate/BNNS/ActivationFunction/sigmoid) An activation function that returns the sigmoid function of its input. [`case silu`](/documentation/Accelerate/BNNS/ActivationFunction/silu) An activation function that returns the sigmoid linear unit (SiLU) function of its input. [`case softShrink(alpha: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/softShrink(alpha:)) An activation function that returns zero when the absolute input is less than alpha, otherwise it returns its input minus alpha. [`case softmax`](/documentation/Accelerate/BNNS/ActivationFunction/softmax) An activation function that returns the softmax function of its input. [`case softplus(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/softplus(alpha:beta:)) An activation function that returns the softplus function of its input. [`case softsign`](/documentation/Accelerate/BNNS/ActivationFunction/softsign) An activation function that returns the softsign function of its input. [`case tanh`](/documentation/Accelerate/BNNS/ActivationFunction/tanh) An activation function that returns the hyperbolic tangent of its input. [`case tanhShrink`](/documentation/Accelerate/BNNS/ActivationFunction/tanhShrink) An activation function that returns its input minus the hyperbolic tangent of its input. [`case threshold(alpha: Float, beta: Float)`](/documentation/Accelerate/BNNS/ActivationFunction/threshold(alpha:beta:)) An activation function that returns beta if its input is less than a specified threshold, otherwise it returns its input. ### Instance Properties [`var bnnsActivation: BNNSActivation`](/documentation/Accelerate/BNNS/ActivationFunction/bnnsActivation) The underlying activation function. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)