pzextr.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 PZEXTR(IEST, XEST, YEST(), YZ(), DY(), NV, NUSE)
    Static X(11), QCOL(10, 7)
    NCOL = 7
    NMAX = 10
    Dim D(10)
    X(IEST) = XEST
    For J = 1 To NV
        DY(J) = YEST(J)
        YZ(J) = YEST(J)
    Next J
    If IEST = 1 Then
        For J = 1 To NV
            QCOL(J, 1) = YEST(J)
        Next J
    Else
        M1 = IEST
        If IEST > NUSE Then M1 = NUSE
        For J = 1 To NV
            D(J) = YEST(J)
        Next J
        For K1 = 1 To M1 - 1
            DELTA = 1# / (X(IEST - K1) - XEST)
            F1 = XEST * DELTA
            F2 = X(IEST - K1) * DELTA
            For J = 1 To NV
                Q = QCOL(J, K1)
                QCOL(J, K1) = DY(J)
                DELTA = D(J) - Q
                DY(J) = F1 * DELTA
                D(J) = F2 * DELTA
                YZ(J) = YZ(J) + DY(J)
            Next J
        Next K1
        For J = 1 To NV
            QCOL(J, M1) = DY(J)
        Next J
    End If
    Erase D
End Sub