1.列主元gauss消去法.cpp

列主元Gauss消去法

#define N 3
#include <stdio.h>
void main()
{    double a[N][N+1],b,m,X[N],sum=0,max;
     int i,j,k;
     printf("please input the data:\n");
     for(i=0;i<=N-1;i++) /*shu ru zeng guang ju zhen*/
     for(j=0;j<=N;j++)
	{ scanf("%lf",&b);
      a[i][j]=b;
	}
     for(i=0;i<=N-1;i++) /*shu chu ju zhen*/
     for(j=0;j<=N;j++)
	{  printf("%lf ",a[i][j]);
       if((j+1)%(N+1)==0)
       printf("\n");
	}
printf("\n");
     for(k=0;k<=N-2;k++) /*zuo xia san jiao ju zhen*/
	{
      max=a[k][k]; /*lie zhu yuan*/
     for(j=0;j<=N;j++)
     for(i=k+1;i<=N-1;i++)
	{   if(a[i][j]>max) max=a[i][j];}
        i=i-1;
        for(j=k;j<=N;j++) /*dui huan */
		{  max=a[i][j];
           a[i][j]=a[k][j];
           a[k][j]=max;
		}
if(a[k][k]!=0) /*xiao qu*/
        for(i=k+1;i<=N-1;i++)
		{   m=a[i][k]/a[k][k];
            for(j=k;j<=N;j++)
            a[i][j]=a[i][j]-m*a[k][j];
		}
	}
        for(i=0;i<=N-1;i++) /*shu chu xia san jiao ju zhen*/
        for(j=0;j<=N;j++)
		{ printf("%lf ",a[i][j]);
           if((j+1)%(N+1)==0)
           printf("\n");
		}
printf("\n");
X[N-1]=a[N-1][N]/a[N-1][N-1]; /*qiu chu X*/
        for(k=N-2;k>=0;k--)
		{ for(j=k+1;j<=N-1;j++)
          sum+=a[k][j]*X[j];
          X[k]=(a[k][N]-sum)/a[k][k];
          sum=0;
		}
   for(i=0;i<=N-1;i++) /*shu chu x*/
   printf("X[%d]=%lf ",i+1,X[i]);
   printf("\n");
}