Extract variables from function

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1

Hi everyone, here is my code :

class Variables : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.variables)


    fun main(args: Array<Double>) {


        fun rungeKutta4(t0: Double, tp: Double, h: Double, f: F, g: G, z: Z) {



            var t = t0
            var x = 0.0
            var xp = 0.0
            var y = 0.0
            var yp = 0.0
            var xna = 0.0
            var xnap = 0.0


            val p = ((tp-t0)/h).toInt()

            **val tv = mutableListOf(t)**

** val xv = mutableListOf(x)**
** val xnav = mutableListOf(xna)**
** val yv = mutableListOf(y)**

            for (i in 0..p) {


                if (i == p) break


                val K1 = f(t,x,xp,y,yp)
                val L1 = g(x,xp,y,yp)
                val M1 = z(t,xna,xnap)
                val Kx = h*xp/2.0 + h*h*K1/8.0
                val Ky = h*yp/2.0 + h*h*L1/8.0
                val Kxna = h*xna/2.0 + h*h*M1/8.0
                val K2 = f(t+h/2.0,x+Kx,xp+h*K1/2.0,y+Ky,yp+h*L1/2.0)
                val L2 = g(x+Kx,xp+h*K1/2.0,y+Ky,yp+h*L1/2.0)
                val M2 = z(t+h/2.0,xna+Kxna,xnap+h*M1/2.0)
                val K3 = f(t+h/2.0,x+Kx,xp+h*K2/2.0,y+Ky,yp+h*L2/2.0)
                val L3 = g(x+Kx,xp+h*K2/2.0,y+Ky,yp+h*L2/2.0)
                val M3 = z(t+h/2.0,xna+Kxna,xnap+h*M2/2.0)
                val Lx = h*xp + h*h*K3/2.0
                val Ly = h*yp + h*h*L3/2.0
                val Lxna = h*xnap + h*h*M3/2.0
                val K4 = f(t+h,x+Lx,xp+h*K3,y+Ly,yp+h*L3)
                val L4 = g(x+Lx,xp+h*K3,y+Ly,yp+h*L3)
                val M4 = z(t+h,xna+Lxna,xnap+h*M3)

                x += h*xp + h*h*(K1+K2+K3)/6.0
                xp += h*(K1+2.0*K2+2.0*K3+K4)/6.0
                y += h*yp + h*h*(L1+L2+L3)/6.0
                yp += h*(L1+2.0*L2+2.0*L3+L4)/6.0
                xna += h*xnap + h*h*(M1+M2+M3)/6.0
                xnap += h*(M1+2.0*M2+2.0*M3+M4)/6.0
                t += h

                tv.add(t)
                xv.add(x)
                xnav.add(xna)
                yv.add(y)

            }
        }

        val F = intent.getStringExtra("F").toDouble()
        val m1 = intent.getStringExtra("m1").toDouble()
        val m2 = intent.getStringExtra("m2").toDouble()
        val k1 = intent.getStringExtra("k1").toDouble()
        val k3 = intent.getStringExtra("k3").toDouble()
        val c1 = intent.getStringExtra("c1").toDouble()
        val c2 = intent.getStringExtra("c2").toDouble()

        val f = fun(t: Double, x: Double, xp: Double, y: Double, yp: Double) = (1.0/m1)*(F * cos(sqrt(k1/m1)*t) -k1*x-k3*(x-y)-c1*xp-c2*(xp-yp))
        val g = fun(x: Double, xp: Double, y: Double, yp: Double) = (1.0/m2)*(k3*(x-y)+c2*(xp-yp))
        val z = fun(t: Double, xna: Double, xnap: Double) = (1.0/m1)*(F* cos(sqrt(k1/m1) *t) -k1*xna-c1*xnap)

        rungeKutta4(0.0, 10.0, 0.1, f, g, z)

    }

**I want to extract the variables tv, xv, xnav, yv (in bold in the code) from the function rungeKutta4 in order to use them in another function, how can I proceed ? **

Thanks for your help :slight_smile:

Samet