4.5 对称正定矩阵的求逆 ssgj.c

来自「许士良常用算法程序集C语言,包括c++一些常用算法代码」· C语言 代码 · 共 40 行

#include "stdlib.h"
#include "math.h"
#include "stdio.h"
int ssgj(a,n)
int n;
double a[];
{ 
	int i,j,k,m;
    double w,g,*b;
    b=malloc(n*sizeof(double));
    for (k=0; k<=n-1; k++)
    { 
		w=a[0];
        if (fabs(w)+1.0==1.0)
        { 
			free(b); 
			printf("fail\n"); 
			return(-2);
		}
        m=n-k-1;
        for (i=1; i<=n-1; i++)
        { 
			g=a[i*n]; b[i]=g/w;
            if (i<=m) b[i]=-b[i];
            for (j=1; j<=i; j++)
				a[(i-1)*n+j-1]=a[i*n+j]+g*b[j];
        }
        a[n*n-1]=1.0/w;
        for (i=1; i<=n-1; i++)
			a[(n-1)*n+i-1]=b[i];
    }
    for (i=0; i<=n-2; i++)
		for (j=i+1; j<=n-1; j++)
			a[i*n+j]=a[j*n+i];
    free(b);
    return(2);
}