LayerNorm

LayerNorm performs a layer normalization operation on src tensor.

The layerNorm operation performs normalization from begin_norm_axis to last dimension of the data tensor. It is defined by the following formulas which is the same as Layer normalization.

\[\dst(t, n, c) = \gamma(c) \cdot \frac{\src(t, n, c) - \mu(t, n)} {\sqrt{\sigma^2(t, n) + \epsilon}} + \beta(c),\]

where

• \(\gamma(c), \beta(c)\) are optional scale and shift for a channel

• \(\mu(t, n), \sigma^2(t, n)\) are mean and variance (see

• \(\epsilon\) is a constant to improve numerical stability.

Mean and variance are computed at runtime or provided by a user. When mean and variance are computed at runtime, the following formulas are used:

• \(\mu(t, n) = \frac{1}{C} \sum\limits_{c} \src(t, n, c)_{}\),

• \(\sigma^2(t, n) = \frac{1}{C} \sum\limits_{c} {}_{} (\src(t, n, c) - \mu(t, n))^2\).

Operation Attributes

Attribute Name	Description	Value Type	Supported Values	Required or Optional
keep_stats	Indicate whether to output mean and variance which can be later passed to backward op	bool	false, true (default)	Optional
begin_norm_axis	begin_norm_axis is used to indicate which axis to start layer normalization. The normalization is from begin_norm_axis to last dimension. Negative values means indexing from right to left. This op normalizes over the last dimension by default, e.g. C in TNC for 3D and LDNC for 4D.	s64	[-r,r-1],where r=rank(src). -1 is default	Optional
use_affine	When set to True, this module has learnable per-element affine parameters.	bool	false, true (default)	Optional
epsilon	The constant to improve numerical stability	f32	Arbitrary positive f32 value, 1e-5 (default)	Optional

Execution Arguments

The inputs and outputs must be provided according to the below index order when constructing an operation.

Inputs

Index	Argument Name	Required or Optional
0	src	Required
1	gamma	Optional
2	beta	Optional

@note gamma is scaling for normalized value. beta is the bias added to the scaled normalized value. They are both 1D tensor with the same span as src’s channel axis and required if attribute use_affine is set to True.

Outputs

Index	Argument Name	Required or Optional
0	dst	Required
1	mean	Optional
2	variance	Optional

@note Both mean and variance are required if attribute keep_stats is set to True.

Supported Data Types

LayerNorm operation supports the following data type combinations.

Src / Dst	Gamma / Beta / Mean / Variance
f32	f32
bf16	f32, bf16
f16	f32