TrendLineクラスを使用してデータの傾向を示す近似曲線を描画した場合、その曲線の係数はTrendLineクラスのCoefficientsコレクションを用いて取得することができます。

以下に、３次多項式を用いた近似曲線の係数を取得し、その多項式をフォームのタイトルバーに表示するサンプルコードを記載します。



◎サンプルコード（VB）

Imports C1.Win.Chart

Public Class Form1

    Private tLine1 As C1.Win.Chart.TrendLine
    Dim tLineOrder As Integer = 3

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ' シリーズの作成
        Dim series1 As New C1.Win.Chart.Series()
        series1.BindingX = "X"
        series1.Binding = "Y"
        series1.DataSource = New System.Drawing.Point() {
            New System.Drawing.Point(1, 50),
            New System.Drawing.Point(2, 38),
            New System.Drawing.Point(3, 42),
            New System.Drawing.Point(4, 30),
            New System.Drawing.Point(5, 27),
            New System.Drawing.Point(6, 25),
            New System.Drawing.Point(7, 33),
            New System.Drawing.Point(8, 35),
            New System.Drawing.Point(9, 30),
            New System.Drawing.Point(10, 40)}
        series1.ChartType = C1.Chart.ChartType.Scatter

        ' 近似曲線用シリーズの作成
        tLine1 = New C1.Win.Chart.TrendLine()
        tLine1.BindingX = "X"
        tLine1.Binding = "Y"
        tLine1.ChartType = C1.Chart.ChartType.Line
        tLine1.FitType = C1.Chart.FitType.Polynom
        tLine1.Order = tLineOrder
        tLine1.DataSource = series1.DataSource

        ' チャートの設定
        FlexChart1.Series.Clear()
        FlexChart1.Series.Add(series1)
        FlexChart1.Series.Add(tLine1)
    End Sub

    Private Sub FlexChart1_Rendered(sender As Object, e As RenderEventArgs) Handles FlexChart1.Rendered
        ' 近似曲線の係数を取得
        For i As Integer = 0 To tLine1.Coefficients.Length - 1
            Console.WriteLine("{0}", tLine1.Coefficients(i))
        Next

        ' 近似曲線の数式の設定
        Dim tLine As TrendLine = FlexChart1.Series(1)
        Dim result As String = String.Format("{1:+0.0000;-0.0000;+0}x{0:+0.0000;-0.0000;+0}", tLine.Coefficients(0), tLine.Coefficients(1))
        For i As Integer = 2 To tLineOrder
            result = result.Insert(0, String.Format("{0:+0.000;-0.0000;+0}x^{1}", tLine.Coefficients(i), i))
        Next
        result = result.Remove(0, 1).Insert(0, "y=")

        ' 取得した数式の表示
        Me.Text = result
        Console.WriteLine(result)
    End Sub
End Class

◎サンプルコード（C#）

using C1.Win.Chart;

namespace prj_FlexChart
{
    public partial class Form1 : Form
    {
        //private C1.Win.Chart.TrendLine tLine1;
        private C1.Win.Chart.TrendLine tLine1;
        int tLineOrder = 3;

        public Form1()
        {
            InitializeComponent();

            // シリーズの作成
            C1.Win.Chart.Series series1 = new C1.Win.Chart.Series();
            series1.BindingX = "X";
            series1.Binding = "Y";
            series1.DataSource = new System.Drawing.Point[] { 
                new System.Drawing.Point(1, 50), 
                new System.Drawing.Point(2, 38), 
                new System.Drawing.Point(3, 42), 
                new System.Drawing.Point(4, 30), 
                new System.Drawing.Point(5, 27), 
                new System.Drawing.Point(6, 25), 
                new System.Drawing.Point(7, 33), 
                new System.Drawing.Point(8, 35), 
                new System.Drawing.Point(9, 30), 
                new System.Drawing.Point(10, 40) };
            series1.ChartType = C1.Chart.ChartType.Scatter;

            // 近似曲線用シリーズの作成
            tLine1 = new C1.Win.Chart.TrendLine();
            tLine1.BindingX = "X";
            tLine1.Binding = "Y";
            tLine1.ChartType = C1.Chart.ChartType.Line;
            tLine1.FitType = C1.Chart.FitType.Polynom;
            tLine1.Order = tLineOrder;
            tLine1.DataSource = series1.DataSource;

            // チャートの設定
            flexChart1.Series.Clear();
            flexChart1.Series.Add(series1);
            flexChart1.Series.Add(tLine1);
        }

        private void flexChart1_Rendered(object sender, RenderEventArgs e)
        {
            // 近似曲線の係数を取得
            for (int i = 0; i <= tLine1.Coefficients.Length - 1; i++)
                Console.WriteLine("{0}", tLine1.Coefficients[i]);

            // 近似曲線の数式の設定
            TrendLine tLine = (TrendLine)flexChart1.Series[1];
            string result = string.Format("{1:+0.0000;-0.0000;+0}x{0:+0.0000;-0.0000;+0}", tLine.Coefficients[0], tLine.Coefficients[1]);
            for (int i = 2; i <= tLineOrder; i++)
                result = result.Insert(0, string.Format("{0:+0.000;-0.0000;+0}x^{1}", tLine.Coefficients[i], i));
            result = result.Remove(0, 1).Insert(0, "y=");

            // 取得した数式の表示
            this.Text = result;
            Console.WriteLine(result);
        }
    }
}