1. Sinc(x)訊號繪圖

namespace Q1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            textBox1.Text = "-15";
            textBox2.Text = "15";
        }

        double sinc(double x)
        {
            if (x == 0) return 1;
            return Math.Sin(x) / x;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            panel1.Refresh();
        }

        private void panel1_Paint(object sender, PaintEventArgs e)
        {
            var l = int.Parse(textBox1.Text);
            var r = int.Parse(textBox2.Text);

            double m = double.MaxValue, M = double.MinValue;

            var h = 300;
            var w = 800;
            var my = (panel1.Height - h) / 2;
            var mx = (panel1.Width - w) / 2;

            var mid = w / (r - l) * -l;

            PointF? lastDot = null;
            for (decimal x = l; x <= r; x += 0.1m)
            {
                var v = (sinc((double)x));
                var p = new PointF((int)(mx + (x + Math.Abs(l)) * (w / (r - l))),
                       (int)(my + (1 - v) * h / 6 * 5));
                if (x % 5 == 0)
                {
                    e.Graphics.DrawString(((int)x).ToString(),
                          new Font(FontFamily.GenericSerif, 14), Brushes.Black,
 p.X, my + h / 6 * 5);
                    e.Graphics.DrawLine(new Pen(Brushes.Black, 2),
                        p.X, my + h / 6 * 5, p.X, my + h / 6 * 5 - 4);
                }

                if (x % 1 == 0)
                {
                    e.Graphics.DrawLine(new Pen(Brushes.Black, 2),
          p.X, my + h / 6 * 5, p.X, my + h / 6 * 5 - 2);
                }

                if (lastDot != null)
                {
                    e.Graphics.DrawLine(new Pen(Brushes.Red, 2),
                      p, lastDot.Value);
                }
                lastDot = p;
                if (v < m) m = v;
                if (v > M) M = v;
            }

            //MessageBox.Show($"{m:f1}/{M:f1}");

            e.Graphics.DrawLine(new Pen(Brushes.Black, 2),// x
                mx + -20, my + h / 6 * 5, mx + w, my + h / 6 * 5);
            e.Graphics.DrawLine(new Pen(Brushes.Black, 2),  // y
                mx + mid, my - 15, mx + mid, my + h + 15);

            for (int i = 0; i < 5; i++)
            {
                e.Graphics.DrawString($"{1 - (0.2 * i):f1}",
                    new Font(FontFamily.GenericSerif, 14), Brushes.Black,
                    mx + mid - 40, my + h / 6 * (i) - 5);
            }
            e.Graphics.DrawString($"{-0.2:f1}",
    new Font(FontFamily.GenericSerif, 14), Brushes.Black,
   mx + mid - 40, my + h - 20);


            for (int i = 0; i <= 30; i++)
            {
                if (i % 5 == 0)
                    e.Graphics.DrawLine(new Pen(Brushes.Black, 2),
                     mx + mid, my + (int)((double)h * i / 30),
                   mx + mid + 4, my + (int)((double)h * i / 30));

                e.Graphics.DrawLine(new Pen(Brushes.Black, 2),
                 mx + mid, my + (int)((double)h * i / 30),
               mx + mid + 2, my + (int)((double)h * i / 30));
            }
        }
    }
}