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"
)

// ReduceSum is an operator to perform reduce-sum function.
type ReduceSum[O mat.Tensor] struct {
    x O
}

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

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

// Forward computes the output of this function.
func (r *ReduceSum[O]) Forward() (mat.Tensor, error) {
    return r.x.Value().(mat.Matrix).Sum(), nil
}

// Backward computes the backward pass.
func (r *ReduceSum[O]) Backward(gy mat.Tensor) error {
    if !mat.IsScalar(gy) {
        return fmt.Errorf("fn: the gradient had to be a scalar")
    }
    if r.x.RequiresGrad() {
        x := r.x.Value()
        gx := x.(mat.Matrix).NewMatrix(mat.WithShape(x.Size()), mat.WithBacking(mat.CreateInitializedSlice(x.Size(), gy.Item().F64())))
        r.x.AccGrad(gx)
    }
    return nil
}