#include "math.h"
  void hhbg(n,a)
  int n;
  double a[];
  { int i,j,k,u,v;
    double d,t;
    for (k=1; k<=n-2; k++)
      { d=0.0;
        for (j=k; j<=n-1; j++)
          { u=j*n+k-1; t=a[u];
            if (fabs(t)>fabs(d))
              { d=t; i=j;}
          }
        if (fabs(d)+1.0!=1.0)
          { if (i!=k)
              { for (j=k-1; j<=n-1; j++)
                  { u=i*n+j; v=k*n+j;
                    t=a[u]; a[u]=a[v]; a[v]=t;
                  }
                for (j=0; j<=n-1; j++)
                  { u=j*n+i; v=j*n+k;
                    t=a[u]; a[u]=a[v]; a[v]=t;
                  }
              }
            for (i=k+1; i<=n-1; i++)
              { u=i*n+k-1; t=a[u]/d; a[u]=0.0;
                for (j=k; j<=n-1; j++)
                  { v=i*n+j;
                    a[v]=a[v]-t*a[k*n+j];
                  }
                for (j=0; j<=n-1; j++)
                  { v=j*n+k;
                    a[v]=a[v]+t*a[j*n+i];
                  }
              }
          }
      }
    return;
  }