/* The functions in this file return bessel functions */

#include <bessel_2.h>


void sphbes(int n, double x, double *sj, double *sy,
	    double *sjp, double *syp)
{
	double factor,order,rj,rjp,ry,ryp;

	order=n+0.5;
	bessjy(x,order,&rj,&ry,&rjp,&ryp);
	factor=RTPIO2/sqrt(x);
	*sj = factor * rj;
	*sy = factor * ry;
	*sjp = factor * rjp-(*sj)/(2.0*x);
	*syp = factor * ryp-(*sy)/(2.0*x);
}


void bessjy(double x, double xnu, double *rj, double *ry,
	    double *rjp, double *ryp)
{
	int i,isign,l,nl;
	double a,b,br,bi,c,cr,ci,d,del,del1,den,di,dlr,dli,dr,e,f,fact,fact2,
		fact3,ff,gam,gam1,gam2,gammi,gampl,h,p,pimu,pimu2,q,r,rjl,
		rjl1,rjmu,rjp1,rjpl,rjtemp,ry1,rymu,rymup,rytemp,sum,sum1,
		temp,w,x2,xi,xi2,xmu,xmu2;

	nl=(x < XMIN ? (int)(xnu+0.5) : IMAX(0,(int)(xnu-x+1.5)));
	xmu=xnu-nl;
	xmu2=xmu*xmu;
	xi=1.0/x;
	xi2=2.0*xi;
	w=xi2/PI;
	isign=1;
	h=xnu*xi;
	if (h < FPMIN) h=FPMIN;
	b=xi2*xnu;
	d=0.0;
	c=h;
	for (i=1;i<=MAXIT;i++) {
		b += xi2;
		d=b-d;
		if (fabs(d) < FPMIN) d=FPMIN;
		c=b-1.0/c;
		if (fabs(c) < FPMIN) c=FPMIN;
		d=1.0/d;
		del=c*d;
		h=del*h;
		if (d < 0.0) isign = -isign;
		if (fabs(del-1.0) < EPS) break;
	}
	rjl=isign*FPMIN;
	rjpl=h*rjl;
	rjl1=rjl;
	rjp1=rjpl;
	fact=xnu*xi;
	for (l=nl;l>=1;l--) {
		rjtemp=fact*rjl+rjpl;
		fact -= xi;
		rjpl=fact*rjtemp-rjl;
		rjl=rjtemp;
	}
	if (rjl == 0.0) rjl=EPS;
	f=rjpl/rjl;
	if (x < XMIN) {
		x2=0.5*x;
		pimu=PI*xmu;
		fact = (fabs(pimu) < EPS ? 1.0 : pimu/sin(pimu));
		d = -log(x2);
		e=xmu*d;
		fact2 = (fabs(e) < EPS ? 1.0 : sinh(e)/e);
		beschb(xmu,&gam1,&gam2,&gampl,&gammi);
		ff=2.0/PI*fact*(gam1*cosh(e)+gam2*fact2*d);
		e=exp(e);
		p=e/(gampl*PI);
		q=1.0/(e*PI*gammi);
		pimu2=0.5*pimu;
		fact3 = (fabs(pimu2) < EPS ? 1.0 : sin(pimu2)/pimu2);
		r=PI*pimu2*fact3*fact3;
		c=1.0;
		d = -x2*x2;
		sum=ff+r*q;
		sum1=p;
		for (i=1;i<=MAXIT;i++) {
			ff=(i*ff+p+q)/(i*i-xmu2);
			c *= (d/i);
			p /= (i-xmu);
			q /= (i+xmu);
			del=c*(ff+r*q);
			sum += del;
			del1=c*p-i*del;
			sum1 += del1;
			if (fabs(del) < (1.0+fabs(sum))*EPS) break;
		}
		rymu = -sum;
		ry1 = -sum1*xi2;
		rymup=xmu*xi*rymu-ry1;
		rjmu=w/(rymup-f*rymu);
	} else {
		a=0.25-xmu2;
		p = -0.5*xi;
		q=1.0;
		br=2.0*x;
		bi=2.0;
		fact=a*xi/(p*p+q*q);
		cr=br+q*fact;
		ci=bi+p*fact;
		den=br*br+bi*bi;
		dr=br/den;
		di = -bi/den;
		dlr=cr*dr-ci*di;
		dli=cr*di+ci*dr;
		temp=p*dlr-q*dli;
		q=p*dli+q*dlr;
		p=temp;
		for (i=2;i<=MAXIT;i++) {
			a += 2*(i-1);
			bi += 2.0;
			dr=a*dr+br;
			di=a*di+bi;
			if (fabs(dr)+fabs(di) < FPMIN) dr=FPMIN;
			fact=a/(cr*cr+ci*ci);
			cr=br+cr*fact;
			ci=bi-ci*fact;
			if (fabs(cr)+fabs(ci) < FPMIN) cr=FPMIN;
			den=dr*dr+di*di;
			dr /= den;
			di /= -den;
			dlr=cr*dr-ci*di;
			dli=cr*di+ci*dr;
			temp=p*dlr-q*dli;
			q=p*dli+q*dlr;
			p=temp;
			if (fabs(dlr-1.0)+fabs(dli) < EPS) break;
		}
		gam=(p-f)/q;
		rjmu=sqrt(w/((p-f)*gam+q));
		rjmu=SIGN(rjmu,rjl);
		rymu=rjmu*gam;
		rymup=rymu*(p+q/gam);
		ry1=xmu*xi*rymu-rymup;
	}
	fact=rjmu/rjl;
	*rj=rjl1*fact;
	*rjp=rjp1*fact;
	for (i=1;i<=nl;i++) {
		rytemp=(xmu+i)*xi2*ry1-rymu;
		rymu=ry1;
		ry1=rytemp;
	}
	*ry=rymu;
	*ryp=xnu*xi*rymu-ry1;
}


void beschb(double x, double *gam1, double *gam2, double *gampl,
	    double *gammi)
{
	double xx;
	static double c1[] = {
		-1.142022680371172e0,6.516511267076e-3,
		3.08709017308e-4,-3.470626964e-6,6.943764e-9,
		3.6780e-11,-1.36e-13};
	static double c2[] = {
		1.843740587300906e0,-0.076852840844786e0,
		1.271927136655e-3,-4.971736704e-6,-3.3126120e-8,
		2.42310e-10,-1.70e-13,-1.0e-15};

	xx=8.0*x*x-1.0;
	*gam1=chebev(-1.0,1.0,c1,NUSE1,xx);
	*gam2=chebev(-1.0,1.0,c2,NUSE2,xx);
	*gampl= *gam2-x*(*gam1);
	*gammi= *gam2+x*(*gam1);
}


double chebev(double a, double b, double c[], int m, double x)
{
	double d=0.0,dd=0.0,sv,y,y2;
	int j;

	y2=2.0*(y=(2.0*x-a-b)/(b-a));
	for (j=m-1;j>=1;j--) {
		sv=d;
		d=y2*d-dd+c[j];
		dd=sv;
	}
	return y*d-dd+0.5*c[0];
}