绘制 sigmoid函数

// 用来计算从-4到4之间的sigmoid函数值的静态函数 public   class  Uitility ... {    public static PointF[] GetPoints()    ...{        PointF[] mypos=new PointF[400];        int j=0;        for(double i=-4;i<=4;i+=0.02)        ...{            mypos[j]= new PointF((float)i,(float)Sigmoid(i));            j++;        }        return mypos;    }    public static double Sigmoid(double x)    ...{        return 1/(1+Math.Pow(Math.E,-x));    }} // 调用函数,完成函数的picturebox1上的绘制 Graphics grfx = pictureBox1.CreateGraphics();         int  picwidth = pictureBox1.Width; int  picheight = pictureBox1.Height; float  midx = ( float )picwidth / 2 ; float  midy = ( float )picheight / 2 ;Pen bb = new  Pen(Brushes.Black, 2 );grfx.DrawLine(Pens.Red, new  Point( 0 ,picheight - 1 ), new  Point(picwidth,picheight - 1 )); // 横坐标 grfx.DrawLine(Pens.Red, new  Point(( int )midx,picheight), new  Point(( int )midx, 0 ));PointF[] cc = Uitility.GetPoints();PointF[] realone = new  PointF[cc.Length]; int  cclen = cc.Length;     // 将与坐标无关的数值转换成与坐标相关的点 for ( int  i = 0 ;i < cclen;i ++ ) ... {    float fx=cc[i].X*picwidth/8+midx;    float fy=cc[i].Y*picheight;     realone[i]=new PointF(fx,-fy+picheight);} grfx.DrawLines(bb,realone);