source code
/* The Computer Language Benchmarks Game
https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
contributed by Ralph Ganszky
converted to Swift 3 by Daniel Muellenborn
*/
import Glibc
import Dispatch
// Get matrix dimension
let n: Int
if CommandLine.arguments.count > 1 {
n = Int(CommandLine.arguments[1]) ?? 5500
} else {
n = 5500
}
let queue = DispatchQueue.global(qos: .default)
func A(_ i: Int, _ j: Int) -> Double {
return 1.0 / Double((i+j)*(i+j+1)/2 + (i+1))
}
func multiplyAv(_ n: Int, _ v: [Double]) -> [Double] {
var Av = [Double](repeating: 0.0, count: n)
DispatchQueue.concurrentPerform(iterations: n) { i in
var AvTemp = 0.0
for j in 0..<n {
AvTemp += A(i,j) * v[j]
}
Av[i] = AvTemp // This is unprotected and could cause
// a problem. Maybe here some atomic update
// or a semaphore should be used
}
return Av
}
func multiplyAtv(_ n: Int, _ v: [Double]) -> [Double] {
var Atv = [Double](repeating: 0.0, count: n)
DispatchQueue.concurrentPerform(iterations: n) { i in
var AtvTemp = 0.0
for j in 0..<n {
AtvTemp += A(j,i) * v[j]
}
Atv[i] = AtvTemp
}
return Atv
}
func multiplyAtAv(_ n: Int, _ v: [Double]) -> [Double] {
let u = multiplyAv(n, v)
return multiplyAtv(n, u)
}
func approximate(_ n: Int) -> Double {
var u = [Double](repeating: 1.0, count: n)
var v = [Double]()
for _ in 0..<10 {
v = multiplyAtAv(n, u)
u = multiplyAtAv(n, v)
}
var vBv = 0.0
var vv = 0.0
for i in 0..<n {
vBv += u[i]*v[i]
vv += v[i]*v[i]
}
return sqrt(vBv/vv)
}
func roundDouble(_ num: Double, precision: Int) -> String {
let exponent = pow(10.0, Double(precision))
let number = Double(Int(num * exponent + 0.5))/exponent
return "\(number)"
}
print(roundDouble(approximate(n), precision: 9))
notes, command-line, and program output
NOTES:
64-bit Ubuntu quad core
Swift version 5.10
(swift-5.10-RELEASE)
Fri, 08 Mar 2024 02:16:10 GMT
MAKE:
/opt/src/swift-5.10-RELEASE/usr/bin/swiftc spectralnorm.swift-3.swift -Ounchecked -o spectralnorm.swift-3.swift_run
14.43s to complete and log all make actions
COMMAND LINE:
./spectralnorm.swift-3.swift_run 5500
PROGRAM OUTPUT:
1.274224153