// Public domain code from Yi-Kuo Yu & Stephen Altschul, NCBI

#include <math.h>

#define TINY 1.0e-20;

void ludcmp(a,n,indx,d)
int n,*indx;
double **a,*d;
{
	int i,imax,j,k;
	double big,dum,sum,temp;
	double *vv,*dvector();
	void nrerror(),free_dvector();

	vv=dvector(1,n);
	*d=1.0;
	for (i=1;i<=n;i++) {
		big=0.0;
		for (j=1;j<=n;j++)
			if ((temp=fabs(a[i][j])) > big) big=temp;
		if (big == 0.0) nrerror("Singular matrix in routine LUDCMP");
		vv[i]=1.0/big;
	}
	for (j=1;j<=n;j++) {
		for (i=1;i<j;i++) {
			sum=a[i][j];
			for (k=1;k<i;k++) sum -= a[i][k]*a[k][j];
			a[i][j]=sum;
		}
		big=0.0;
		for (i=j;i<=n;i++) {
			sum=a[i][j];
			for (k=1;k<j;k++)
				sum -= a[i][k]*a[k][j];
			a[i][j]=sum;
			if ( (dum=vv[i]*fabs(sum)) >= big) {
				big=dum;
				imax=i;
			}
		}
		if (j != imax) {
			for (k=1;k<=n;k++) {
				dum=a[imax][k];
				a[imax][k]=a[j][k];
				a[j][k]=dum;
			}
			*d = -(*d);
			vv[imax]=vv[j];
		}
		indx[j]=imax;
		if (a[j][j] == 0.0) a[j][j]=TINY;
		if (j != n) {
			dum=1.0/(a[j][j]);
			for (i=j+1;i<=n;i++) a[i][j] *= dum;
		}
	}
	free_dvector(vv,1,n);
}

#undef TINY
