111.绘制正态分布曲线

  

   

    

     

    
    

     

      #include "stdio.h"
     
    
   

    

     

    
    

     

      #include "math.h"
     
    
   

    

     

    
    

     

      #include "graphics.h"
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      double lgam1(x) /*Gamma函数的计算*/
     
    
   

    

     

    
    

     

      double x;
     
    
   

    

     

    
    

     

      { 
     
    
   

    

     

    
    

     
	int i;
     
    
   

    

     

    
    

     
    double y,t,s,u;
     
    
   

    

     

    
    

     
    static double a[11]={ 0.0000677106,-0.0003442342,
     
    
   

    

     

    
    

     
		0.0015397681,-0.0024467480,0.0109736958,
     
    
   

    

     

    
    

     
		-0.0002109075,0.0742379071,0.0815782188,
     
    
   

    

     

    
    

     
		0.4118402518,0.4227843370,1.0};
     
    
   

    

     

    
    

     
    if (x<=0.0)
     
    
   

    

     

    
    

     

      	{ printf("err**x<=0!\n"); return(-1.0);}
     
    
   

    

     

    
    

     

          y=x;
     
    
   

    

     

    
    

     
    if (y<=1.0)
     
    
   

    

     

    
    

     

      	{
     
    
   

    

     

    
    

     

      		t=1.0/(y*(y+1.0)); y=y+2.0;}
     
    
   

    

     

    
    

     
    else if (y<=2.0)
     
    
   

    

     

    
    

     

      	{ 
     
    
   

    

     

    
    

     

      		t=1.0/y; y=y+1.0;}
     
    
   

    

     

    
    

     
    else if (y<=3.0) t=1.0;
     
    
   

    

     

    
    

     
    else
     
    
   

    

     

    
    

     

      	{ 
     
    
   

    

     

    
    

     

      		t=1.0;
     
    
   

    

     

    
    

     
        while (y>3.0)
     
    
   

    

     

    
    

     

      		{ y=y-1.0; t=t*y;}
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     

          s=a[0]; u=y-2.0;
     
    
   

    

     

    
    

     
    for (i=1; i<=10; i++)
     
    
   

    

     

    
    

     

      		s=s*u+a[i];
     
    
   

    

     

    
    

     

          s=s*t;
     
    
   

    

     

    
    

     
    return(s);
     
    
   

    

     

    
    

     

      }  
     
    
   

    

     

    
    

     

      double lgam2(a,x) /*不完全Gamma函数*/
     
    
   

    

     

    
    

     

      double a,x;
     
    
   

    

     

    
    

     

      { 
     
    
   

    

     

    
    

     
	int n;
     
    
   

    

     

    
    

     
    double p,q,d,s,s1,p0,q0,p1,q1,qq;
     
    
   

    

     

    
    

     
    if ((a<=0.0)||(x<0.0))
     
    
   

    

     

    
    

     

      	{ if (a<=0.0) printf("err**a<=0!\n");
     
    
   

    

     

    
    

     
	if (x<0.0) printf("err**x<0!\n");
     
    
   

    

     

    
    

     
	return(-1.0);
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
    if (x+1.0==1.0) return(0.0);
     
    
   

    

     

    
    

     
    if (x>1.0e+35) return(1.0);
     
    
   

    

     

    
    

     

          q=log(x); q=a*q; qq=exp(q);
     
    
   

    

     

    
    

     
    if (x<1.0+a)
     
    
   

    

     

    
    

     

      	{ 
     
    
   

    

     

    
    

     

      		p=a; d=1.0/a; s=d;
     
    
   

    

     

    
    

     
        for (n=1; n<=100; n++)
     
    
   

    

     

    
    

     

      		{ 
     
    
   

    

     

    
    

     

      			p=1.0+p; d=d*x/p; s=s+d;
     
    
   

    

     

    
    

     
			if (fabs(d)<fabs(s)*1.0e-07)
     
    
   

    

     

    
    

     

      			{ 
     
    
   

    

     

    
    

     

      				s=s*exp(-x)*qq/lgam1(a);
     
    
   

    

     

    
    

     
                return(s);
     
    
   

    

     

    
    

     

      			}
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
    else
     
    
   

    

     

    
    

     

      	{ 
     
    
   

    

     

    
    

     

      		s=1.0/x; p0=0.0; p1=1.0; q0=1.0; q1=x;
     
    
   

    

     

    
    

     
        for (n=1; n<=100; n++)
     
    
   

    

     

    
    

     

      		{ 
     
    
   

    

     

    
    

     

      			p0=p1+(n-a)*p0; q0=q1+(n-a)*q0;
     
    
   

    

     

    
    

     

                  p=x*p0+n*p1; q=x*q0+n*q1;
     
    
   

    

     

    
    

     
            if (fabs(q)+1.0!=1.0)
     
    
   

    

     

    
    

     

      			{ 
     
    
   

    

     

    
    

     

      				s1=p/q; p1=p; q1=q;
     
    
   

    

     

    
    

     
                if (fabs((s1-s)/s1)<1.0e-07)
     
    
   

    

     

    
    

     

      				{ 
     
    
   

    

     

    
    

     

      					s=s1*exp(-x)*qq/lgam1(a);
     
    
   

    

     

    
    

     
                    return(1.0-s);
     
    
   

    

     

    
    

     

      				}
     
    
   

    

     

    
    

     

                      s=s1;
     
    
   

    

     

    
    

     

      			}
     
    
   

    

     

    
    

     

                  p1=p; q1=q;
     
    
   

    

     

    
    

     

      		}
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
    printf("a too large !\n");
     
    
   

    

     

    
    

     

          s=1.0-s*exp(-x)*qq/lgam1(a);
     
    
   

    

     

    
    

     
    return(s);
     
    
   

    

     

    
    

     

      }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      double lerrf(x) /*误差函数*/
     
    
   

    

     

    
    

     

      double x;
     
    
   

    

     

    
    

     

      { 
     
    
   

    

     

    
    

     
	double y;
     
    
   

    

     

    
    

     
    if (x>=0.0)
     
    
   

    

     

    
    

     

      		y=lgam2(0.5,x*x);
     
    
   

    

     

    
    

     
    else
     
    
   

    

     

    
    

     

      		y=-lgam2(0.5,x*x);
     
    
   

    

     

    
    

     
    return(y);
     
    
   

    

     

    
    

     

      }
     
    
   

    

     

    
    

     

      double lgass(a,d,x) /*正态分布函数*/
     
    
   

    

     

    
    

     

      double a,d,x;
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     
	double y;
     
    
   

    

     

    
    

     
    if (d<=0.0) d=1.0e-10;
     
    
   

    

     

    
    

     

          y=0.5+0.5*lerrf((x-a)/(sqrt(2.0)*d));
     
    
   

    

     

    
    

     
    return(y);
     
    
   

    

     

    
    

     

      }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      main()
     
    
   

    

     

    
    

     

      { 
     
    
   

    

     

    
    

     
	int i;
     
    
   

    

     

    
    

     
	double j;
     
    
   

    

     

    
    

     
    double a, d;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
	int gdriver = DETECT, gmode;
     
    
   

    

     

    
    

     
	clrscr();
     
    
   

    

     

    
    

     
	printf("This program will draw the Normal Distribution Graph.\n");
     
    
   

    

     

    
    

     
	printf("Please input the mathematical expectation (Alpha): ");
     
    
   

    

     

    
    

     
	scanf("%lf", &a );
     
    
   

    

     

    
    

     
	printf("Please input the variance (Sita >0): ");
     
    
   

    

     

    
    

     
	scanf("%lf", &d );
     
    
   

    

     

    
    

     
	/*registerbgidriver( EGAVGA_driver );*/
     
    
   

    

     

    
    

     
	initgraph( &gdriver, &gmode, "e:\\tc\\bgi" );
     
    
   

    

     

    
    

     
	
     
    
   

    

     

    
    

     
	setbkcolor( BLUE );
     
    
   

    

     

    
    

     
	moveto( 50, 430 );
     
    
   

    

     

    
    

     
	lineto( 590, 430 );
     
    
   

    

     

    
    

     
	outtextxy( 600, 425, "X");
     
    
   

    

     

    
    

     
	moveto( 200, 50 );
     
    
   

    

     

    
    

     
	lineto( 200, 450 );
     
    
   

    

     

    
    

     
	outtextxy( 200, 30, "Y" );
     
    
   

    

     

    
    

     
	outtextxy( 185, 435, "O");
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
	setcolor( RED );
     
    
   

    

     

    
    

     
	moveto( 51, 430 - 100 * lgass( a, d, -150.0 ) );
     
    
   

    

     

    
    

     
	for( i = 51; i <= 590; i++ )
     
    
   

    

     

    
    

     

      	{
     
    
   

    

     

    
    

     

      		j = 430 - 360 * lgass( a, d, (double)(i-200) );
     
    
   

    

     

    
    

     
		lineto( i, j );
     
    
   

    

     

    
    

     

      	}
     
    
   

    

     

    
    

     
	getch();
     
    
   

    

     

    
    

     
	closegraph();
     
    
   

    

     

    
    

     

      }
     
    
  
 

文章来源: blog.csdn.net，作者：程序员编程指南，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/weixin_41055260/article/details/124576365