Main Content

Batch normalization layer

A batch normalization layer normalizes a mini-batch of data across all observations for each channel independently. To speed up training of the convolutional neural network and reduce the sensitivity to network initialization, use batch normalization layers between convolutional layers and nonlinearities, such as ReLU layers.

After normalization, the layer scales the input with a learnable scale factor
*γ* and shifts by a learnable offset *β*.

creates a batch normalization layer.`layer`

= batchNormalizationLayer

creates a batch normalization layer and sets the optional `layer`

= batchNormalizationLayer(`Name,Value`

)`TrainedMean`

, `TrainedVariance`

, `Epsilon`

, Parameters and Initialization, Learn Rate and Regularization, and
`Name`

properties using one or more name-value pairs.
For example, `batchNormalizationLayer('Name','batchnorm')`

creates a batch normalization layer with the name
`'batchnorm'`

.

The batch normalization operation normalizes the elements
*x _{i}* of the input by first calculating the mean

$$\widehat{{x}_{i}}=\frac{{x}_{i}-{\mu}_{B}}{\sqrt{{\sigma}_{B}^{2}+\u03f5}},$$

where *ϵ* is a constant that improves numerical
stability when the variance is very small.

To allow for the possibility that inputs with zero mean and unit variance are not optimal for the operations that follow batch normalization, the batch normalization operation further shifts and scales the activations using the transformation

$${y}_{i}=\gamma {\widehat{x}}_{i}+\beta ,$$

where the offset *β* and scale factor
*γ* are learnable parameters that are updated during network
training.

To make predictions with the network after training, batch normalization requires a fixed mean and variance to normalize the data. This fixed mean and variance can be calculated from the training data after training, or approximated during training using running statistic computations.

If the `'BatchNormalizationStatistics'`

training option is `'moving'`

, then the software approximates the batch normalization statistics during training using a running estimate and, after training, sets the `TrainedMean`

and `TrainedVariance`

properties to the latest values of the moving estimates of the mean and variance, respectively.

If the `'BatchNormalizationStatistics'`

training option is `'population'`

, then after network training finishes, the software passes through the data once more and sets the `TrainedMean`

and `TrainedVariance`

properties to mean and variance computed from the entire training data set, respectively.

The layer uses the `TrainedMean`

and `TrainedVariance`

to normalize the input during prediction.

[1] Ioffe, Sergey, and Christian Szegedy. "Batch normalization: Accelerating deep
network training by reducing internal covariate shift." *preprint,
arXiv:1502.03167* (2015).

`convolution2dLayer`

| `fullyConnectedLayer`

| `groupNormalizationLayer`

| `layerNormalizationLayer`

| `reluLayer`

| `trainingOptions`

| `trainNetwork`