Step by Step solution about How to resolve the algorithm Active object step by step in the Go programming language

Overview:

• The code implements an "active integrator" class aio that continuously integrates an input function k(t) over time and stores the result in a state variable s.
• The integrator runs as a separate goroutine to handle the integration process asynchronously.

Components:

1. Type Definitions:

type tFunc func(time.Duration) float64
type aio struct {
   iCh chan tFunc        // channel for setting input function
   oCh chan chan float64 // channel for requesting output
}

• tFunc represents the input function that takes a time duration and returns a float64 value.
• aio is the active integrator object. It manages the input and output channels for controlling the integration function and obtaining the integrated value.

2. Constructor:

func newAio() *aio {
   var a aio
   a.iCh = make(chan tFunc)
   a.oCh = make(chan chan float64)
   go aif(&a)
   return &a
}

• newAio() creates an instance of the active integrator and starts a goroutine aif that runs the integration process.

3. Input Method:

func (a aio) input(f tFunc) {
   a.iCh <- f
}

• input allows the user to set the input function f that will be integrated.

4. Output Method:

func (a aio) output() float64 {
   sCh := make(chan float64)
   a.oCh <- sCh
   return <-sCh
}

• output returns the current integrated value of s by sending a channel to the aif goroutine and receiving the value back.

5. Integration Function:

func aif(a *aio) {
   var k tFunc = zeroFunc // integration function
   s := 0.                // "object state" initialized to 0
   t0 := time.Now()       // initial time
   k0 := k(0)             // initial sample value
   t1 := t0               // t1, k1 used for trapezoid formula
   k1 := k0

   tk := time.Tick(10 * time.Millisecond) // 10 ms -> 100 Hz
   for {
       select {
       case t2 := <-tk: // timer tick event
           k2 := k(t2.Sub(t0))                        // new sample value
           s += (k1 + k2) * .5 * t2.Sub(t1).Seconds() // trapezoid formula
           t1, k1 = t2, k2                            // save time and value
       case k = <-a.iCh: // input method event: function change
       case sCh := <-a.oCh: // output method event: sample object state
           sCh <- s
       }
   }
}

• aif is the goroutine that continuously integrates the input function.
• It uses a 10 ms timer to sample the input function at 100 Hz.
• It calculates the integral using the trapezoid formula.

Main Function:

func main() {
   a := newAio()                           // create object
   a.input(func(t time.Duration) float64 { // 1. set input to sin function
       return math.Sin(t.Seconds() * math.Pi)
   })
   time.Sleep(2 * time.Second) // 2. sleep 2 sec
   a.input(zeroFunc)           // 3. set input to zero function
   time.Sleep(time.Second / 2) // 4. sleep .5 sec
   fmt.Println(a.output())     // output should be near zero
}

• The main function sets up the integration by creating an aio instance and configuring the input function to be a sine wave.
• It sleeps for 2 seconds and then changes the input function to zero.
• Finally, it prints the integrated value after sleeping for another 0.5 seconds. The output should be close to zero since the input function becomes zero.

package main

import (
    "fmt"
    "math"
    "time"
)

// type for input function, k.
// input is duration since an arbitrary start time t0.
type tFunc func(time.Duration) float64

// active integrator object.  state variables are not here, but in
// function aif, started as a goroutine in the constructor.
type aio struct {
    iCh chan tFunc        // channel for setting input function
    oCh chan chan float64 // channel for requesting output
}

// constructor
func newAio() *aio {
    var a aio
    a.iCh = make(chan tFunc)
    a.oCh = make(chan chan float64)
    go aif(&a)
    return &a
}

// input method required by task description.  in practice, this method is
// unnecessary; you would just put that single channel send statement in
// your code wherever you wanted to set the input function.
func (a aio) input(f tFunc) {
    a.iCh <- f
}

// output method required by task description.  in practice, this method too
// would not likely be best.  instead any client interested in the value would
// likely make a return channel sCh once, and then reuse it as needed.
func (a aio) output() float64 {
    sCh := make(chan float64)
    a.oCh <- sCh
    return <-sCh
}

// integration function that returns constant 0
func zeroFunc(time.Duration) float64 { return 0 }

// goroutine serializes access to integrated function k and state variable s
func aif(a *aio) {
    var k tFunc = zeroFunc // integration function
    s := 0.                // "object state" initialized to 0
    t0 := time.Now()       // initial time
    k0 := k(0)             // initial sample value
    t1 := t0               // t1, k1 used for trapezoid formula
    k1 := k0

    tk := time.Tick(10 * time.Millisecond) // 10 ms -> 100 Hz
    for {
        select {
        case t2 := <-tk: // timer tick event
            k2 := k(t2.Sub(t0))                        // new sample value
            s += (k1 + k2) * .5 * t2.Sub(t1).Seconds() // trapezoid formula
            t1, k1 = t2, k2                            // save time and value
        case k = <-a.iCh: // input method event: function change
        case sCh := <-a.oCh: // output method event: sample object state
            sCh <- s
        }
    }
}

func main() {
    a := newAio()                           // create object
    a.input(func(t time.Duration) float64 { // 1. set input to sin function
        return math.Sin(t.Seconds() * math.Pi)
    })
    time.Sleep(2 * time.Second) // 2. sleep 2 sec
    a.input(zeroFunc)           // 3. set input to zero function
    time.Sleep(time.Second / 2) // 4. sleep .5 sec
    fmt.Println(a.output())     // output should be near zero
}