// Copyright 2019 The TensorFlow Authors. All Rights Reserved.
//
// Licensed 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 "AS IS" BASIS,
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/// A numerical optimizer.
///
/// Optimizers apply an optimization algorithm to update the differentiable models.
public protocol Optimizer {
    /// The type of the model whose parameters are optimized.
    associatedtype Model: Differentiable
    /// The scalar parameter type.
    associatedtype Scalar: FloatingPoint
    /// The learning rate.
    var learningRate: Scalar { get set }
    /// Updates the specified differentiable variables along the specified direction.
    mutating func update(_ variables: inout Model, along direction: Model.TangentVector)
}
