<— 4__Model_components.md	Зміст	4_2_Linear_layers.md —>

4.1 The notion of layer

We call layers standard complex compounded tensor operations that have been designed and empirically identified as being generic and efficient. They often incorporate trainable parameters and correspond to a convenient level of granularity for designing and describing large deep models. The term is inherited from simple multi-layer neural networks, even though modern models may take the form of a complex graph of such modules, incorporating multiple parallel pathways.

In the following pages, I try to stick to the convention for model depiction illustrated above:

• operators / layers are depicted as boxes,
• darker coloring indicates that they embed trainable parameters,
• non-default valued meta-parameters are added in blue on their right,
• a dashed outer frame with a multiplicative factor indicates that a group of layers is replicated in series, each with its own set of trainable parameters if any, and
• in some cases, the dimension of their output is specified on the right when it differs from their input.

Additionally, layers that have a complex internal structure are depicted with a greater height.