rkdumb.txt

用VB实现解常微分方程组 包括定步长四阶龙格-库塔法、自适应变步长的龙格-库塔法、改进的中点法、外推法等

Sub RKDUMB(VSTART(), NVAR, X1, X2, NSTEP, XX(), Y())
    Dim V(10), DV(10)
    For I = 1 To NVAR
        V(I) = VSTART(I)
        Y(I, 1) = V(I)
    Next I
    XX(1) = X1
    X = X1
    H = (X2 - X1) / CSng(NSTEP)
    For K = 1 To NSTEP
        Call DERIVS(X, V(), DV())
        Call RK4(V(), DV(), NVAR, X, H, V)
        If X + H = X Then
            Print " Stepsize not signficant in RKDUMB."
            Exit Sub
        End If
        X = X + H
        XX(K + 1) = X
        For I = 1 To NVAR
            Y(I, K + 1) = V(I)
        Next I
    Next K
    Erase DV, V
End Sub