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);