swift之如何编写一个函数来对 n 维向量进行点积

首先，这里有一个关于 dot product 的简短提醒是。

我希望能够有一段代码，我可以按以下方式使用它:

 let x = Vector<Double>(dimensions: 3) 
 let y = Vector<Double>(dimensions: 3) 
 
 //... 
 //assign some values (coordinates) to x and y 
 //x.dotProduct(y) 

如何将dotProduct 实现为类 方法？

这是不起作用的:

func dot(vector: Point<T>) -> Double { 
    var sum: Double = 0.0 
    for index in 0...vector.size { 
       sum += sum + vector[index] * point[index] 
    } 
} 

错误信息是:

error: cannot invoke '*' with an argument list of type '(@lvalue T, $T14)' 

新函数点:

 func dot(vector: Point<T>) -> T { 
    var sum = 0 as T 
    println(point.count) 
 
    for index in 0..<point.count{ 
        println(vector[index]) 
        println(point[index]) 
 
        sum += vector[index] * point[index] 
    } 
 
    return sum 
} 

请您参考如下方法:

更新 4:

这个有效:

class Vector<T: SummableMultipliable> { 
    var dimensions: Int 
    var coordinates: [T] 
 
    init(dimensions: Int) { 
        self.dimensions = dimensions 
        self.coordinates = [T](count: dimensions, repeatedValue: 0 as T) 
    } 
 
    func dotProduct<T>(vector: Vector<T>) -> T { 
        assert(self.dimensions == vector.dimensions, "Vectors don't have the same dimensions.") 
 
        //as @AirspeedVelocity suggested: 
        return reduce(Zip2(self.coordinates, vector.coordinates), 0) { sum, pair in sum + pair.0 * pair.1 } 
 
        //the old version: 
        /*var sum: T = 0 
 
        for dimension in 0..<self.dimensions { 
            sum = sum + (self.coordinates[dimension] as T * vector.coordinates[dimension]) 
        } 
 
        return sum*/ 
    } 
} 
 
protocol SummableMultipliable: Equatable, IntegerLiteralConvertible { 
    func +(lhs: Self, rhs: Self) -> Self 
    func *(lhs: Self, rhs: Self) -> Self 
} 
 
extension Int: SummableMultipliable { } 
extension Double: SummableMultipliable { } 
 
var x = Vector<Int>(dimensions: 3) 
var y = Vector<Int>(dimensions: 3) 
 
x.coordinates[0] = 3 
x.coordinates[1] = 2 
x.coordinates[2] = 1 
 
y.coordinates[0] = 3 
y.coordinates[1] = 2 
y.coordinates[2] = 1 
 
println(x.dotProduct(y)) //prints 14