`sub`¶

Elementwise difference of two tensors with identical shapes.

Category: arithmetic · Identity: sub@1

Shape¶

a[B, ...], b[B, ...] -> out[B, ...]

Port	Direction	Pattern	dtype
`a`	input	`a[B, ...]`	compute
`b`	input	`b[B, ...]`	compute
`out`	output	`out[B, ...]`	compute

Arguments¶

This operator takes no scalar arguments.

Description¶

out = a - b with no broadcasting; the two operands must agree on rank, every axis extent, and dtype, and the difference is computed in the plan compute dtype. Order matters, so both tensor inputs must be supplied explicitly: sub(h, saved) is h - saved.

Examples¶

Example 1¶

A residual that subtracts the shortcut; both inputs are explicit.

saved = x
linear(8, name="branch")
relu()
h = linear(4)
sub(h, saved)

Input ['B', 4] → output ['B', 4].

Network: [B, 4] -> [B, 4]  dtype=float32
index  name    operation  input shapes        output shapes
0      branch  linear     x=[B, 4]            out=[B, 8]
1      n1      relu       x=[B, 8]            out=[B, 8]
2      n2      linear     x=[B, 8]            out=[B, 4]
3      n3      sub        a=[B, 4], b=[B, 4]  out=[B, 4]

Parameters: 76

Example 2¶

Sequences work too: the two halves of the feature axis are differenced.

a, b = split(4, dim=2)
sub(a, b)

Input ['B', 6, 8] → output ['B', 6, 4].

Network: [B, 6, 8] -> [B, 6, 4]  dtype=float32
index  name  operation  input shapes              output shapes
0      n0    split      x=[B, 6, 8]               first=[B, 6, 4], rest=[B, 6, 4]
1      n1    sub        a=[B, 6, 4], b=[B, 6, 4]  out=[B, 6, 4]

Parameters: 0

Example 3¶

Images: the operand shapes must match exactly.

saved = x
conv(3, kernel_size=3, padding=1)
h = tanh()
sub(h, saved)

Input ['B', 3, 8, 8] → output ['B', 3, 8, 8].

Network: [B, 3, 8, 8] -> [B, 3, 8, 8]  dtype=float32
index  name  operation  input shapes                    output shapes
0      n0    conv       x=[B, 3, 8, 8]                  out=[B, 3, 8, 8]
1      n1    tanh       x=[B, 3, 8, 8]                  out=[B, 3, 8, 8]
2      n2    sub        a=[B, 3, 8, 8], b=[B, 3, 8, 8]  out=[B, 3, 8, 8]

Parameters: 84

sub¶