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"
)

// Div is an operator to perform element-wise division over two values.
type Div[O mat.Tensor] struct {
    x1 O
    x2 O
}

// NewDiv returns a new Div Function.
func NewDiv[O mat.Tensor](x1 O, x2 O) *Div[O] {
    return &Div[O]{
        x1: x1,
        x2: x2,
    }
}

// Operands returns the list of operands.
func (r *Div[O]) Operands() []mat.Tensor {
    return []mat.Tensor{r.x1, r.x2}
}

// Forward computes the output of the function.
func (r *Div[O]) Forward() (mat.Tensor, error) {
    return r.x1.Value().(mat.Matrix).Div(r.x2.Value().(mat.Matrix)), nil
}

// Backward computes the backward pass.
func (r *Div[O]) Backward(gy mat.Tensor) error {
    x1v := r.x1.Value().(mat.Matrix)
    x2v := r.x2.Value().(mat.Matrix)
    if !mat.SameDims(x1v, gy.(mat.Matrix)) || !mat.SameDims(x2v, gy.(mat.Matrix)) {
        return fmt.Errorf("fn: matrices have incompatible dimensions")
    }
    if r.x1.RequiresGrad() {
        gx := gy.(mat.Matrix).Div(r.x2.Value().(mat.Matrix))
        r.x1.AccGrad(gx)
    }
    if r.x2.RequiresGrad() {
        x2sq := r.x2.Value().(mat.Matrix).Prod(r.x2.Value().(mat.Matrix))
        gx := r.x1.Value().(mat.Matrix).Prod(gy.(mat.Matrix))
        gx.ProdScalarInPlace(-1)
        gx.DivInPlace(x2sq)
        r.x2.AccGrad(gx)
    }
    return nil
}