mat/gradfn/log.go
// Copyright 2022 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"
)
// Log is an operator to perform element-wise natural logarithm function.
type Log[O mat.Tensor] struct {
x O
}
// NewLog returns a new Log Function.
func NewLog[O mat.Tensor](x O) *Log[O] {
return &Log[O]{
x: x,
}
}
// Operands returns the list of operands.
func (l *Log[O]) Operands() []mat.Tensor {
return []mat.Tensor{l.x}
}
// Forward computes the output of the function.
func (l *Log[O]) Forward() (mat.Tensor, error) {
return l.x.Value().(mat.Matrix).Log(), nil
}
// Backward computes the backward pass.
func (l *Log[O]) Backward(gy mat.Tensor) error {
if !mat.SameDims(l.x.Value(), gy) {
return fmt.Errorf("fn: matrices have incompatible dimensions")
}
if l.x.RequiresGrad() {
gx := l.x.Value().(mat.Matrix).Apply(safeLogDeriv)
gx.ProdInPlace(gy.(mat.Matrix))
l.x.AccGrad(gx)
}
return nil
}
func safeLogDeriv(_, _ int, v float64) float64 {
if v > 0.0 {
return 1.0 / v
}
if v == 0.0 {
return 1.0 / 1.0e-08
}
panic("ag: invalid log for negative values")
}