Mobile architect.

// Distance from signal strength (log-distance model)
fun distance(rssi: Int, tx: Int = -59, n: Double = 2.0) =
    10.0.pow((tx - rssi) / (10 * n))

// Where the phone is, from three beacons
fun trilaterate(a: Beacon, b: Beacon, c: Beacon): Point {
    val A = 2 * (b.x - a.x); val B = 2 * (b.y - a.y)
    val C = a.r.sq - b.r.sq - a.x.sq + b.x.sq - a.y.sq + b.y.sq
    val D = 2 * (c.x - b.x); val E = 2 * (c.y - b.y)
    val F = b.r.sq - c.r.sq - b.x.sq + c.x.sq - b.y.sq + c.y.sq
    return Point((C*E - F*B) / (A*E - B*D), (A*F - C*D) / (A*E - B*D))
}