Created
April 17, 2019 04:08
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extension Array where Element: Differentiable { | |
/// Views the array as the differentiable product manifold of `Element` with itself `count` times. | |
public struct DifferentiableView: Differentiable { | |
/// The array that we are viewing. | |
public var base: [Element] | |
/// Construct a view of the given array. | |
public init(_ base: [Element]) { self.base = base } | |
// MARK: - Differentiable conformance. | |
public typealias TangentVector = Array<Element.TangentVector>.DifferentiableView | |
public typealias CotangentVector = Array<Element.CotangentVector>.DifferentiableView | |
public typealias AllDifferentiableVariables = Array<Element.AllDifferentiableVariables>.DifferentiableView | |
public var allDifferentiableVariables: AllDifferentiableVariables { | |
get { | |
return AllDifferentiableVariables(base.map { $0.allDifferentiableVariables }) | |
} | |
set(v) { | |
precondition(base.count == v.base.count, "count mismatch") | |
for i in base.indices { | |
base[i].allDifferentiableVariables = v.base[i] | |
} | |
} | |
} | |
public func moved(along direction: TangentVector) -> DifferentiableView { | |
precondition(base.count == direction.base.count, "count mismatch") | |
return DifferentiableView(zip(base, direction.base).map { $0.moved(along: $1) }) | |
} | |
public func tangentVector(from cotangentVector: CotangentVector) -> TangentVector { | |
precondition(base.count == cotangentVector.base.count, "count mismatch") | |
return TangentVector(zip(base, cotangentVector.base).map { | |
(selfElement, cotangentVectorElement) in | |
selfElement.tangentVector(from: cotangentVectorElement) | |
}) | |
} | |
} | |
} | |
extension Array.DifferentiableView: KeyPathIterable {} | |
extension Array.DifferentiableView: Equatable where Element: Equatable { | |
public static func == (lhs: Array.DifferentiableView, rhs: Array.DifferentiableView) -> Bool { | |
return lhs.base == rhs.base | |
} | |
} | |
/// Makes `Array.DifferentiableView` additive as the product space. | |
/// | |
/// Note that `Array.DifferentiableView([])` is the zero in the product spaces of all counts. | |
extension Array.DifferentiableView: AdditiveArithmetic where Element: AdditiveArithmetic { | |
public static var zero: Array.DifferentiableView { return Array.DifferentiableView([]) } | |
public static func + (lhs: Array.DifferentiableView, rhs: Array.DifferentiableView) -> Array.DifferentiableView { | |
precondition(lhs.base.count == 0 || rhs.base.count == 0 || lhs.base.count == rhs.base.count, "count mismatch") | |
if lhs.base.count == 0 { | |
return rhs | |
} | |
if rhs.base.count == 0 { | |
return lhs | |
} | |
return Array.DifferentiableView(zip(lhs.base, rhs.base).map(+)) | |
} | |
public static func - (lhs: Array.DifferentiableView, rhs: Array.DifferentiableView) -> Array.DifferentiableView { | |
precondition(lhs.base.count == 0 || rhs.base.count == 0 || lhs.base.count == rhs.base.count, "count mismatch") | |
if lhs.base.count == 0 { | |
return rhs | |
} | |
if rhs.base.count == 0 { | |
return lhs | |
} | |
return Array.DifferentiableView(zip(lhs.base, rhs.base).map(-)) | |
} | |
} | |
/// Makes `Array` differentiable as the product manifold of `Element` with itself `count` times. | |
/// | |
/// This is a convenience wrapper around `Array.DifferentiableView`. | |
extension Array: Differentiable where Element: Differentiable { | |
public typealias TangentVector = Array<Element.TangentVector>.DifferentiableView | |
public typealias CotangentVector = Array<Element.CotangentVector>.DifferentiableView | |
public typealias AllDifferentiableVariables = Array<Element.AllDifferentiableVariables>.DifferentiableView | |
public var allDifferentiableVariables: AllDifferentiableVariables { | |
get { | |
return DifferentiableView(self).allDifferentiableVariables | |
} | |
set(v) { | |
var view = DifferentiableView(self) | |
view.allDifferentiableVariables = v | |
self = view.base | |
} | |
} | |
public func moved(along direction: TangentVector) -> Array { | |
return DifferentiableView(self).moved(along: direction).base | |
} | |
public func tangentVector(from cotangentVector: CotangentVector) -> TangentVector { | |
return DifferentiableView(self).tangentVector(from: cotangentVector) | |
} | |
} |
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