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"
)

// Flatten is a Function to reshape a matrix-operand into a "flattened" row vector.
type Flatten[O mat.Tensor] struct {
    x O
}

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

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

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

// Backward computes the backward pass.
func (r *Flatten[O]) Backward(gy mat.Tensor) error {
    if !(mat.IsVector(gy) && r.x.Value().Size() == gy.Size()) {
        return fmt.Errorf("fn: matrices have incompatible dimensions")
    }
    if r.x.RequiresGrad() {
        gx := gy.(mat.Matrix).Reshape(r.x.Value().Shape()...)
        r.x.AccGrad(gx)
    }
    return nil
}