Gaussian elimination: Difference between revisions

=={{header|Swift}}==

{{trans|Rust}}

<lang swift>func gaussEliminate(_ sys: [[Double]]) -> [Double]? {

var system = sys

let size = system.count

for i in 0..<size-1 where system[i][i] != 0 {

for j in i..<size-1 {

let factor = system[j + 1][i] / system[i][i]

for k in i..<size+1 {

system[j + 1][k] -= factor * system[i][k]

}

}

}

for i in (1..<size).reversed() where system[i][i] != 0 {

for j in (1..<i+1).reversed() {

let factor = system[j - 1][i] / system[i][i]

for k in (0..<size+1).reversed() {

system[j - 1][k] -= factor * system[i][k]

}

}

}

var solutions = [Double]()

for i in 0..<size {

guard system[i][i] != 0 else {

return nil

}

system[i][size] /= system[i][i]

system[i][i] = 1

solutions.append(system[i][size])

}

return solutions

}

let sys = [

[1.00, 0.00, 0.00, 0.00, 0.00, 0.00, -0.01],

[1.00, 0.63, 0.39, 0.25, 0.16, 0.10, 0.61],

[1.00, 1.26, 1.58, 1.98, 2.49, 3.13, 0.91],

[1.00, 1.88, 3.55, 6.70, 12.62, 23.80, 0.99],

[1.00, 2.51, 6.32, 15.88, 39.90, 100.28, 0.60],

[1.00, 3.14, 9.87, 31.01, 97.41, 306.02, 0.02]

]

guard let sols = gaussEliminate(sys) else {

fatalError("No solutions")

}

for (i, f) in sols.enumerated() {

print("X\(i + 1) = \(f)")

}</lang>

{{out}}

<pre>X1 = -0.01

X2 = 1.6027903945021138

X3 = -1.613203059905563

X4 = 1.245494121371438

X5 = -0.4909897195846575

X6 = 0.065760696175232</pre>