Sub pivotize(m() As Double, im() As Double)
    Dim As Integer n, i, j
    n = Ubound(m)
    Redim im(n, n)

    For i = 0 To n
        For j = 0 To n
            im(i, j) = 0
        Next j
        im(i, i) = 1
    Next i

    For i = 0 To n
        Dim As Double mx
        Dim As Integer fila
        mx = Abs(m(i, i))
        fila = i
        For j = i To n
            If Abs(m(j, i)) > mx Then
                mx = Abs(m(j, i))
                fila = j
            End If
        Next j
        If i <> fila Then
            For j = 0 To n
                Swap im(i, j), im(fila, j)
            Next j
        End If
    Next i
End Sub

Sub LUdecomposition(a() As Double,l() As Double, u() As Double, p() As Double)
    Dim As Integer i, j, k, n
    Dim As Double s
    n = Ubound(a)
    Redim l(n, n), u(n, n), p(n, n)
    Dim As Double b(n, n)
    pivotize(a(), p())

    For i = 0 To n
        For j = 0 To n
            b(i, j) = 0
            For k = 0 To n
                b(i, j) += p(i, k) * a(k, j)
            Next k
        Next j
    Next i

    For j = 0 To n
        l(j, j) = 1
        For i = 0 To j
            s = 0
            For k = 0 To i - 1
                s += u(k, j) * l(i, k)
            Next k
            u(i, j) = b(i, j) - s
        Next i
        For i = j + 1 To n
            s = 0
            For k = 0 To j - 1
                s += u(k, j) * l(i, k)
            Next k
            l(i, j) = (b(i, j) - s) / u(j, j)
        Next i
    Next j
End Sub

Sub showMatrix(a() As Double)
    Dim As Integer i, j
    Dim As String As1
    For i = 0 To Ubound(a, 1)
        For j = 0 To Ubound(a, 2)
            Print Using "###.##### "; a(i, j);
        Next j
        Print
    Next i
    Print
End Sub

Dim As Double A1(2, 2) => {{1, 3, 5}, {2, 4, 7}, {1, 1, 0}}
Dim As Double L1(), U1(), P1()
LUdecomposition(A1(), L1(), U1(), P1())
Print "L1:"
showMatrix(L1())
Print "U1:"
showMatrix(U1())
Print "P1:"
showMatrix(P1())

Dim As Double A2(3, 3) => {{11, 9, 24, 2}, {1, 5, 2, 6}, {3, 17, 18, 1}, {2, 5, 7, 1}}
Dim As Double L2(), U2(), P2()
LUdecomposition(A2(), L2(), U2(), P2())
Print "L2:"
showMatrix(L2())
Print "U2:"
showMatrix(U2())
Print "P2:"
showMatrix(P2())

Sleep