Sign step and activation functions

Activation.swift

func activate(bias: Double, bW: Double, x: [Double], w: [Double]) -> Int {
    var sum = 0.0
    for i in 0..<x.count {
        sum += x[i] * w[i]
    }
    sum += bias * bW
    return step(sum)
}

SignFunction.swift

func sign(z: Double) -> Int {
    // Note that 0 is not considered positive or negative
    return (z > 0) ? 1 : -1
}