nlpodyssey/spago

// Copyright 2019 spaGO Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gradfn

import (
    "fmt"

    "github.com/nlpodyssey/spago/mat"
)

// ELU is an operator to perform the ELU activation function.
// ELU(x) = max(0,x) + min(0,α ∗ (exp(x) − 1))
type ELU[O mat.Tensor] struct {
    x     O
    alpha O // scalar
}

// NewELU returns a new ELU Function.
func NewELU[O mat.Tensor](x O, alpha O) *ELU[O] {
    return &ELU[O]{
        x:     x,
        alpha: alpha,
    }
}

// Operands returns the list of operands.
func (r *ELU[O]) Operands() []mat.Tensor {
    return []mat.Tensor{r.x, r.alpha}
}

// Forward computes the output of the function.
func (r *ELU[O]) Forward() (mat.Tensor, error) {
    y := r.x.Value().(mat.Matrix).ApplyWithAlpha(elu, r.alpha.Value().Item().F64())
    return y, nil
}

// Backward computes the backward pass.
func (r *ELU[O]) Backward(gy mat.Tensor) error {
    if !mat.SameDims(r.x.Value(), gy) {
        return fmt.Errorf("fn: matrices have incompatible dimensions")
    }
    if r.x.RequiresGrad() {
        gx := r.x.Value().(mat.Matrix).ApplyWithAlpha(eluDeriv, r.alpha.Value().Item().F64())
        gx.ProdInPlace(gy.(mat.Matrix))
        r.x.AccGrad(gx)
    }
    return nil
}