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);