Euler method: Difference between revisions

</pre>

=={{header|Swift}}==

{{trans|C}}

<lang swift>import Foundation

let numberFormat = " %7.3f"

let k = 0.07

let initialTemp = 100.0

let finalTemp = 20.0

let startTime = 0

let endTime = 100

func ivpEuler(function: (Double, Double) -> Double, initialValue: Double, step: Int) {

print(String(format: " Step %2d: ", step), terminator: "")

var y = initialValue

for t in stride(from: startTime, through: endTime, by: step) {

if t % 10 == 0 {

print(String(format: numberFormat, y), terminator: "")

}

y += Double(step) * function(Double(t), y)

}

print()

}

func analytic() {

print(" Time: ", terminator: "")

for t in stride(from: startTime, through: endTime, by: 10) {

print(String(format: " %7d", t), terminator: "")

}

print("\nAnalytic: ", terminator: "")

for t in stride(from: startTime, through: endTime, by: 10) {

let temp = finalTemp + (initialTemp - finalTemp) * exp(-k * Double(t))

print(String(format: numberFormat, temp), terminator: "")

}

print()

}

func cooling(t: Double, temp: Double) -> Double {

return -k * (temp - finalTemp)

}

analytic()

ivpEuler(function: cooling, initialValue: initialTemp, step: 2)

ivpEuler(function: cooling, initialValue: initialTemp, step: 5)

ivpEuler(function: cooling, initialValue: initialTemp, step: 10)</lang>

{{out}}

<pre>

Time: 0 10 20 30 40 50 60 70 80 90 100

Analytic: 100.000 59.727 39.728 29.797 24.865 22.416 21.200 20.596 20.296 20.147 20.073

Step 2: 100.000 57.634 37.704 28.328 23.918 21.843 20.867 20.408 20.192 20.090 20.042

Step 5: 100.000 53.800 34.280 26.034 22.549 21.077 20.455 20.192 20.081 20.034 20.014

Step 10: 100.000 44.000 27.200 22.160 20.648 20.194 20.058 20.017 20.005 20.002 20.000