Broadcast

Broadcast  // Operation that produces a tensor based on arg's axes


Description¶

Operation whose output tensor ignores axes not in the arg tensor.

Inputs¶

Name

Element Type

Shape

arg

Any

Any

Attributes¶

Name

Type

Notes

shape

Shape

The shape of the output.

broadcast_axes

AxisSet

Axis positions in shape that are broadcast.

Outputs¶

Name

Element Type

Shape

output

Same as arg

Same as shape

The shape of arg must match shape with elements in broadcast_axes removed.

For example, if arg is $$[a, b, c]$$ then

$\begin{split}\mathtt{Broadcast(arg, Shape{2, 3}, AxisSet{0})} &= \begin{bmatrix} a & b & c\\ a & b & c \end{bmatrix}\\ \mathtt{Broadcast(arg, Shape{3, 2}, AxisSet{1})} &= \begin{bmatrix} a & a\\ b & b\\ c & c \end{bmatrix}\end{split}$

Mathematical Definition¶

For a coordinate $$C$$, let $$p(C)$$ be a coordinate with the axes in broadcast_axes removed. For example, if $$\mathtt{broadcast_axes}=\{1,3\}$$ then $$p([d_0, d_1, d_2, d_3, d_4]) = [d_0, d_2, d_4]$$. Then

$\mathtt{output}_C = \mathtt{arg}_{p(C)}.$

Backprop¶

$\overline{\mathtt{arg}} \leftarrow \mathtt{Sum}(\Delta, \mathtt{broadcast_axes}).$

C++ Interface¶

class Broadcast : public ngraph::op::Op

Operation which “adds” axes to an input tensor, replicating elements from the input as needed along the new axes.

Subclassed by ngraph::op::v0::BroadcastLike

Public Functions

const NodeTypeInfo &get_type_info() const

Returns the NodeTypeInfo for the node’s class. During transition to type_info, returns a dummy type_info for Node if the class has not been updated yet.

Broadcast()

Constructs a broadcast operation.

Broadcast(const Output<Node> &arg, const Shape &shape, const AxisSet &broadcast_axes)

Constructs a broadcast operation.

Parameters
• arg: The input tensor to be broadcast.

• shape: The shape of the output tensor.

• broadcast_axes: The axis positions (0-based) in the result that are being broadcast. The remaining axes in shape must be the same as the shape of arg.

void validate_and_infer_types()

Throws if the node is invalid.

const AxisSet &get_broadcast_axes() const

Return

A set containing the indices of the broadcast axes (0-based).