rk4.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 RK4(Y(), DYDX(), N, X, H, YOUT())
    Dim YT(10), DYT(10), DYM(10)
    HH = H * 0.5
    H6 = H / 6#
    XH = X + HH
    For I = 1 To N
        YT(I) = Y(I) + HH * DYDX(I)
    Next I
    Call DERIVS(XH, YT(), DYT())
    For I = 1 To N
        YT(I) = Y(I) + HH * DYT(I)
    Next I
    Call DERIVS(XH, YT(), DYM())
    For I = 1 To N
        YT(I) = Y(I) + H * DYM(I)
        DYM(I) = DYT(I) + DYM(I)
    Next I
    Call DERIVS(X + H, YT(), DYT())
    For I = 1 To N
        YOUT(I) = Y(I) + H6 * (DYDX(I) + DYT(I) + 2# * DYM(I))
    Next I
    Erase DYM, DYT, YT
End Sub