Ejercicio de las unidades 7 y 8

Método de Runge - Kutta

Dim N As Integer

Function f (ByVal t As Double, ByVal y As Double) As Double

f= t - y

End Function

Sub RungeKutta (ByVal a As Double, ByVal b As Double, ByVal N As Integer, ByVal y0 As Double)

Dim h, k1, k2, k3, k4 As Double 

Dim t, y As Double

Dim i As Integer

h = (b - a) / N

t = a 

y = y0

vt (0) = t

vy (0) = y

For i = 1 To N

       K1= h * f (t,y)

       K2 = h * f (t + h / 2, y + k1 / 2)

       K3 = h * f (t + h/ 2, y + k2 / 2)

       K4 = h * f (t+ h, y + k3)

       Y = y + (1 / 6) * (k1+ 2 * k2 +2 * k3 + k4)

       t = t + h

       vt (i) = t

       vy (i) = y

Next i 

End Sub

Private Sub CmdEvaluar_Click()

tmin = Val (txta.text)

tmax = Val (txtb.Text)

Yinicial = Val (txty0.Text)

N = Val (txtn.Text)

Call Rungekutta (tmin, tmax, N, Yinicial)

Call vertabla

End  sub

Private Sub Vertabla_Click()

Dim f, i As Integer

MSFlexGrid1.Clear

MSFlexGrid1.Rows = 30

MSFlexGrid1.Cols = 2

MSFlexGrid1.FixedCols = 0

MSFlexGrid1.FixedRows = 0

MSFlexGrid1.ColWidth (0) = 750

MSFlexGrid1.ColWidth  (1) = 1100

MSFlexGrid1.TextMatrix (0, 0) = "t"

MSFlexGrid1.TextMatrix (0,1) = "y(t)"

i = 0

For f = 1 To (N + 1)

      MSFlexGrid1.Rows = f + 1

      MSFlexGrid1.TextMatrix (f, 0) = Format $ ( vt (i), "0.000")

      MSFlexGrid1.TextMatrix (f, 1) = Format $ ( vy (i), "0.0000000")

      i = i + 1

Next f

End Sub

Private Sub CmdSalir_Click()

Unload Me

End Sub