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# Licensed to the Apache Software Foundation (ASF) under one
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# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
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# KIND, either express or implied. See the License for the
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# under the License.
"""
MLP(input, spec; hidden_activation = :relu, prefix)
Construct a multi-layer perceptron. A MLP is a multi-layer neural network with
fully connected layers.
# Arguments:
* `input::SymbolicNode`: the input to the mlp.
* `spec`: the mlp specification, a list of hidden dimensions. For example,
`[128, (512, :sigmoid), 10]`. The number in the list indicate the
number of hidden units in each layer. A tuple could be used to specify
the activation of each layer. Otherwise, the default activation will
be used (except for the last layer).
* `hidden_activation::Symbol`: keyword argument, default `:relu`, indicating
the default activation for hidden layers. The specification here could be overwritten
by layer-wise specification in the `spec` argument. Also activation is not
applied to the last, i.e. the prediction layer. See [`Activation`](@ref) for a
list of supported activation types.
* `prefix`: keyword argument, default `gensym()`, used as the prefix to
name the constructed layers.
Returns the constructed MLP.
"""
function MLP(input, spec; hidden_activation::Symbol = :relu, prefix = gensym())
spec = convert(Vector{Union{Int,Tuple}}, spec)
n_layer = length(spec)
for (i, s) in enumerate(spec)
if isa(s, Tuple)
n_unit, act_type = s
else
n_unit = s
act_type = hidden_activation
end
input = FullyConnected(input, name=Symbol(prefix, "fc$i"), num_hidden=n_unit)
if i < n_layer || isa(s, Tuple)
# will not add activation unless the user explicitly specified
input = Activation(input, name=Symbol(prefix, "$act_type$i"), act_type=act_type)
end
end
return input
end