Option Explicit On
Option Strict On
Public Class Form1

    Private Sub ToolStripButton1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ToolStripButton1.Click
        Dim i As Integer
        Dim n As Integer = 2
        Dim a(,) As Double = {{2.0, 3.0, 1.0, 4.0}, {4.0, 1.0, -3.0, -2.0}, {-1.0, 2.0, 2.0, 2.0}}

        Call MATGJ(n, a)

        For i = 0 To n
            Console.WriteLine(CStr(i) & ":" & CStr(a(i, n + 1)))
        Next i

        '連立一次方程式 [a]{x}={y}の解{x}を求める．a(i,j)=[a|y]を入力する
        '入力                      出力結果
        '[a]={ 2, 3, 1} {y}={ 4}   {x}={ 2}
        '    { 4, 1,-3}     {-2}       {-1}
        '    {-1, 2, 2}     { 2]       { 3}

    End Sub

    Private Sub MATGJ(ByVal n As Integer, ByRef a(,) As Double)
        'Gauss-Jordan法による連立一次方程式の解法
        Dim i As Integer
        Dim j As Integer
        Dim k As Integer
        Dim s As Integer
        Dim p As Double
        Dim d As Double
        Dim max As Double
        Dim dumy As Double

        For k = 0 To n
            max = 0.0
            s = k
            For j = k To n
                If Math.Abs(a(j, k)) > max Then
                    max = Math.Abs(a(j, k))
                    s = j
                End If
            Next j
            For j = 0 To n + 1
                dumy = a(k, j)
                a(k, j) = a(s, j)
                a(s, j) = dumy
            Next j
            p = a(k, k)
            For j = k To n + 1
                a(k, j) = a(k, j) / p
            Next j
            For i = 0 To n
                If i <> k Then
                    d = a(i, k)
                    For j = k To n + 1
                        a(i, j) = a(i, j) - d * a(k, j)
                    Next j
                End If
            Next i
        Next k

    End Sub

End Class