To: info-ibmpc@usc-isib.ARPA
Subject: contribution to library
Date: Sat, 17 May 86 17:18:28 -0500
From: James R. Van Zandt <jrv@mitre-bedford.ARPA>

I'd like to submit this program to the library.
-------------------------------------------

SPLINE.C    Generates splines under tension and allows general curves
            and multiple independent curves in the same file.  Text
            input and output files like the UNIX program.  Written in
            C by J. R. Van Zandt, based on algorithms by A.  K.  Cline.

------------------------------------------------------------
NAME
	spline - interpolate using splines under tension

SYNOPSIS
	spline [file] [options]

DESCRIPTION
	Without options, SPLINE reads pairs of numbers (x- and y-values) from
	the standard input (or the given file), generates a smooth curve
	through the points, and writes to the standard output points from the
	smooth curve.  The curve is a spline under tension (see references),
	which is somewhat "tighter" than a cubic spline, and less likely to
	have spurious inflection points.  As with GRAPH, each pair of points
	may optionally be followed by a comment.  If the comment is surrounded
	by quotes "...", it may contain spaces.  The given points, and
	their comments if any, will be included in the output.

	Input lines starting with ";" are written to the beginning of
	the output file but are otherwise ignored.  Blank lines are
	ignored.

	If the -c switch is not used, the input points must be from a function
	- that is, the x values must be strictly increasing.  The
	output points will also be from a function.  (If the -b switch
	is used, this restriction applies only within each segment.)

	If the -c switch is used (indicating a general curve), the
	input points need not be from a function, but each pair of
	points must be separated from the previous pair by a finite
	distance.  (If the -b switch is used, this restriction applies
	only within each segment.)
	
options are:
  -a  [step [start]] Input data contains only y values - generate automatic
  		abscissas at intervals of step (default 1) starting at start
  		(default 0).

  -b 		break the interpolation at each label.  That is, the input
		curve is divided into sections with the last point in
		each section marked by a label (which may be empty:
		"").  A separate interpolating curve is to be found for
		each section.  In this case, the requirements on the
		number of intervals (specified by the -n switch or
		defaulted) and the interpolation range (specified by the 
		-x switch) are applied to each section independently.

  -c            general curve rather than function.  In this case, the curve
  		is parameterized on the polygonal arclength from the
  		first to the last given point, with the whole length
  		scaled to be 1.  Thus, the values min and max for the
  		-x switch should satisfy 0 <= min < max <= 1.

  -n  num       interpolate over num intervals (default is 100)

  -t num	Specify tension in interpolating curve.  Tension of 50 gives
		almost polygonal line, tension of .01 gives almost cubic
		spline.  Default is 1.

  -x [min [max]]   interpolate from min to max only.  min and max should be in
		the range of the given x values, except that if the -c switch
		is used they should satisfy 0 <= min < max <= 1.

  -xl		take log of x values before interpolating, take exponential
   		afterwards (probably necessary if -xl switch is needed for
   		GRAPH)

  -yl		take log of y values before interpolating, take exponential
   		afterwards (probably necessary if -yl switch is needed for
   		GRAPH)

NOTES
	Similar to the Unix routine, except using splines under tension,
	passing labels through, and allowing general curves.

REFERENCES

	A.  K.  Cline, "Scalar- and Planar- Valued Curve Fitting Using
	Splines Under Tension", Communications of the ACM v 17 n 4 p
	218-223 (Apr 74).

	Schweikert, D.  G.  "An interpolation curve using a spline in
	tension", J.  Math.  and Physics v 45 p 312-317 (1966).

AUTHOR
	Copyright (c) 1985  James R. Van Zandt

	Resale forbidden, copying for personal use encouraged.

------------------------------------------------------------
/*	spline - interpolate points in a tabulated function or curve

	Usage...
		spline [file][options]
		options are:
		  -a  [step [start]] automatic abscissas 
		  -b                 break interpolation at each label
		  -c                 general curve 
		  -n  num            interpolate over num intervals 
		  -t  num            tension in interpolating curve 
		  -x  [min [max]]    interpolate from min to max 

	Notes...
		This program fits a smooth curve through a given set of points,
		using the splines under tension introduced by Schweikert [J. 
		Math.  and Physics v 45 pp 312-317 (1966)].  They are similar
		to cubic splines, but are less likely to introduce spurious
		inflection points.

	History...
		21 Sep 85	Added -xl and -yl switches for taking logs
		23 Nov 85	Passing lines starting with ';' unchanged, otherwise
					ignoring them.

	Author...
		Copyright (c) 1985  James R. Van Zandt

		All rights reserved.
		This program may be copied for personal, non-profit use only.

		Based on algorithms by A.  K.  Cline [Communications of the ACM
		v 17 n 4 pp 218-223 (Apr 74)].

*/

#include <stdio.h>
#include <math.h>

#define VERSION "1.2"

#define ENTRIES 200
#define MAXLABELS 50

double *x, *y, *temp, *xp, *yp, *path;
double slp1=0.,slpn=0.,sigma=-1.;
double abscissa=0.;
double abscissa_step=1.;
double xmin=0.;
double xmax=0.;
double curv2(), mylog();

int xlog=0;		/* nonzero if taking log of x values */
int ylog=0;		/* nonzero if taking log of y values */
int debugging=0;
int breaking=0;		/* nonzero if breaking at labels */
int labels=0;		/* number of labels in input data */
int automatic_abscissas=0;
int abscissa_arguments=0;
int curve=0;		/* nonzero if general curve permitted */
int x_arguments=0;
int n;				/* number of entries in x, y, yp, and temp */
int index_array[MAXLABELS];	/* indexes into x and y */
int *p_data=index_array;
int total=100;

FILE file;

char *label_array[MAXLABELS];
char **p_text=label_array;

main(argc,argv) int argc; char **argv;
{	int nn,origin;
	read_data(argc,argv);
	if(breaking && labels)
		{origin=0;
		while(labels--)
			{p_data[0] -= origin;
			nn=p_data[0]+1;
			if(nn) curv0(nn,total);
			origin += nn;
			path += nn;
			x += nn;
			y += nn;
			p_data++;
			p_text++;
			}
		}
	else
		curv0(n,total);
}

curv0(n,requested)
int n,requested;
{	int i, j, each, stop, seg=0, regressing=0;
	double s,ds,xx,yy;

	for(i=1; i<n; i++) if(path[i]<=path[i-1]) regressing++;
	if (regressing || (curve && (xmin<0. || xmax>1.)))
		{			  /* error: echo input */
		for (i=0; i<n; i++)
			{xx=x[i]; if(xlog) xx=exp(xx);
			yy=y[i]; if(ylog) yy=exp(yy);
			printf("%g %g ",xx,yy);
			if(i == p_data[seg]) puts(p_text[seg++]);
			putchar('\n');
			}
		return;
		}
	if(curve) {curv1(path,x,xp,n); curv1(path,y,yp,n);}
	else curv1(x,y,yp,n);
	s=path[0];
	seg=0;
	if(requested<n) requested=n;
	if(x_arguments==2)		/* specific range was requested */
		{s=xmin;
		ds=(xmax-xmin)/requested;
		if(curve) {ds*=path[n-1]; s*=path[n-1];}
		for(i=requested+1; i; i--)
			{value(s,&xx,&yy,n);
			printf("%g %g ",xx,yy);
			if(j==p_data[seg]) puts(p_text[seg++]);
			putchar('\n');
			s+=ds;
			}
		}
	else			/* spline for entire curve was requested */
		{for (i=j=0; j<n-1; j++)
			{stop=requested*(j+1)/(n-1);
			ds=(path[j+1]-path[j])/(stop-i);
			for ( ; i<stop; i++)
				{value(s,&xx,&yy,n);
				printf("%g %g ",xx,yy);
				if(j==p_data[seg]) puts(p_text[seg++]);
				putchar('\n');
				s+=ds;
				}
			}
			xx=x[n-1]; if(xlog) xx=exp(xx);
			yy=y[n-1]; if(ylog) yy=exp(yy);
			printf("%g %g ",xx,yy);
			if(j==p_data[seg]) puts(p_text[seg++]);
			putchar('\n');
		}
}

value(s,q,r,n) double s,*q,*r; int n;
{	if(curve)
		{*q=curv2(path,x,xp,s,n);
		*r=curv2(path,y,yp,s,n);
		}
	else
		{*q=s;
		*r=curv2(x,y,yp,s,n);
		}
	if(xlog) *q=exp(*q);
	if(ylog) *r=exp(*r);
}

read_data(argc,argv) int argc; char **argv;
{	int i,j,length;
	double xx,yy,d,*pd,sum;
	char *s,*t;
#define BUFSIZE 200
	static char buf[BUFSIZE];

	x=path=malloc(ENTRIES*sizeof(double));
	y=malloc(ENTRIES*sizeof(double));
	if(x==0 || y==0) {fprintf(stderr,"can\'t allocate buffer"); exit();}
	if(argc>1 && streq(argv[1],"?")) help();
	if(argc<=1 || *argv[1]=='-') file=stdin;
	else
		{if(argc>1)
			{file=fopen(argv[1],"r");
			if(file==0) {printf("file %s not found\n",argv[1]); exit();}
			argc--; argv++;
			}
		else help();
		}
	argc--; argv++;
	while(argc>0)
		{i=get_parameter(argc,argv);
		argv=argv+i; argc=argc-i;
		}
	if(xlog && !curve)
		{if(x_arguments>1) xmax=mylog(xmax);
		if(x_arguments>=1) xmin=mylog(xmin);
		}
	if(automatic_abscissas && abscissa_arguments<2 && x_arguments>=1)
		abscissa=xmin;
	p_data[0]=-1;
	i=0;
	while(i<ENTRIES)
		{if(fgets(buf,BUFSIZE,file)==0) break;
		t=buf;
		while(*t && isspace(*t)) t++;
		if(*t == 0) continue;		/* skip blank lines */
		buf[strlen(buf)-1]=0;		/* zero out the line feed */
		if(buf[0]==';') {printf("%s\n",buf); continue;}  /* skip comment */
		if(automatic_abscissas)
			{x[i]=abscissa;
			abscissa+=abscissa_step;
			sscanf(buf,"%F",&y[i]);
			if(ylog) y[i]=mylog(y[i]);
			}
		else
			{sscanf(buf,"%F %F",&x[i],&y[i]);
			if(xlog) x[i]=mylog(x[i]);
			if(ylog) y[i]=mylog(y[i]);
			}
		s=buf;                      /* start looking for label */
		while(*s==' ')s++;		/* skip first number */
		while(*s && (*s!=' '))s++;
		if(!automatic_abscissas)	/* skip second number */
			{while(*s==' ')s++;
			while(*s && (*s!=' '))s++;
			}
		while(*s==' ')s++;
		if((length=strlen(s))&&(labels<MAXLABELS))
			{if(*s=='\"')           /* label in quotes */
				{t=s+1;
				while(*t && (*t!='\"')) t++;
				t++;
				}
			else                    /* label without quotes */
				{t=s;
				while(*t && (*t!=' '))t++;
				}
			*t=0;
			length=t-s;
			p_data[labels]=i;
			p_text[labels]=malloc(length+1);
			if(p_text[labels]) strcpy(p_text[labels++],s);
			}
		i++;
		}
	if(breaking && (!labels || p_data[labels-1]!=n-1))
		{p_data[labels]=i-1;
		if(p_text[labels]=malloc(1)) *p_text[labels++]=0;
		}
	n=i;
	yp=malloc(n*sizeof(double));
	temp=malloc(n*sizeof(double));
	if(temp==0 || yp==0) {fprintf(stderr,"can\'t allocate buffer"); exit();}
	if(curve)
		{xp=malloc(n*sizeof(double));
		path=malloc(n*sizeof(double));
		if(xp==0|| path==0) {fprintf(stderr,"can\'t allocate buffer"); exit();}
		path[0]=sum=0.;
		for (i=1; i<n; i++)
			{xx=x[i]-x[i-1];
			yy=y[i]-y[i-1];
			path[i]=(sum+=sqrt(xx*xx + yy*yy));
			}
/*		for(i=0; i<n; i++)
			printf("path[%d]=%g  x[%d]=%g \n",i,path[i],i,x[i]); */
		}
}


/* get_parameter - process one command line option
		(return # parameters used) */
get_parameter(argc,argv) int argc; char **argv;
{	int i;
	if(streq(*argv,"-a"))
		{i=get_double(argc,argv,2,&abscissa_step,&abscissa,&abscissa);
		abscissa_arguments=i-1;
		automatic_abscissas=1;
		return i;
		}
	else if(streq(*argv,"-b")) {breaking=1; return 1;}
	else if(streq(*argv,"-c")) {curve=1; return 1;}
	else if(streq(*argv,"-d")) {debugging=1; return 1;}
	else if(streq(*argv,"-n"))
		{if((argc>1) && numeric(argv[1])) total=atoi(argv[1]);
		if(debugging)printf("%d output pairs",total);
		return 2;
		}
	if(streq(*argv,"-t"))
		{return(get_double(argc,argv,1,&sigma,&abscissa,&abscissa));
		}
	else if(streq(*argv,"-x"))
		{i=get_double(argc,argv,2,&xmin,&xmax,&xmax);
		x_arguments=i-1;
		return i;
		}
	else if(streq(*argv,"-xl")) {xlog++; return 1;}
	else if(streq(*argv,"-yl")) {ylog++; return 1;}
	else gripe(argv);
}

get_double(argc,argv,permitted,a,b,c)
int argc,permitted; char **argv; double *a,*b,*c;
{	int i=1;
	if((permitted--)>0 && (argc>i) && numeric(argv[i])) *a=atof(argv[i++]);
	if((permitted--)>0 && (argc>i) && numeric(argv[i])) *b=atof(argv[i++]);
	if((permitted--)>0 && (argc>i) && numeric(argv[i])) *c=atof(argv[i++]);
	return i;
}

int streq(a,b) char *a,*b;
{	while(*a)
		{if(*a!=*b)return 0;
		a++; b++;
		}
	return 1;
}

gripe_arg(s) char *s;
{	fprintf(stderr,"argument missing for switch %s",s);
	help();
}

gripe(argv) char **argv;
{	fprintf(stderr,*argv); fprintf(stderr," isn\'t a legal argument \n\n");
	help();
}

help()
{	fprintf(stderr,"spline   version %s",VERSION);
	fprintf(stderr,"\nusage: spline [file][options]\n");
	fprintf(stderr,"options are:\n");
	fprintf(stderr,"  -a  [step [start]] automatic abscissas \n");
	fprintf(stderr,"  -b                 break interpolation after each label \n");
	fprintf(stderr,"  -c                 general curve \n");
	fprintf(stderr,"  -n  num            interpolate over num intervals \n");
	fprintf(stderr,"  -t  num            tension in interpolating curve \n");
	fprintf(stderr,"  -x  [min [max]]    interpolate from min to max \n");
	fprintf(stderr,"  -xl                take logs of x values before interpolating \n");
	fprintf(stderr,"  -yl                take logs of y values before interpolating \n");
	exit();
}

numeric(s) char *s;
{	char c;
	while(c=*s++)
		{if((c<='9' && c>='0') || c=='+' || c=='-' || c=='.') continue;
		return 0;
		}
	return 1;
}

curv1(x,y,yp,n) double *x,*y,*yp; int n;
{	int i;
	double c1,c2,c3,deln,delnm1,delnn,dels,delx1,delx2,delx12;
	double diag1,diag2,diagin,dx1,dx2,exps;
	double sigmap,sinhs,sinhin,slpp1,slppn,spdiag;

	delx1=x[1] - x[0];
	dx1=(y[1] - y[0])/delx1;
	if(sigma >= 0.) {slpp1=slp1; slppn=slpn;}
	else
		{if(n!=2)
			{delx2= x[2] - x[1];
			delx12= x[2] - x[0];
			c1= -(delx12 + delx1)/delx12/delx1;
			c2= delx12/delx1/delx2;
			c3= -delx1/delx12/delx2;
			slpp1= c1*y[0] + c2*y[1] + c3*y[2];
			deln= x[n-1] - x[n-2];
			delnm1= x[n-2] - x[n-3];
			delnn= x[n-1] - x[n-3];
			c1= (delnn + deln)/delnn/deln;
			c2= -delnn/deln/delnm1;
			c3= deln/delnn/delnm1;
			slppn= c3*y[n-3] + c2*y[n-2] + c1*y[n-1];
			}
		else yp[0]=yp[1]=0.;
		}
			/* denormalize tension factor */
	sigmap=fabs(sigma)*(n-1)/(x[n-1]-x[0]);
			/* set up right hand side and tridiagonal system for
			   yp and perform forward elimination	*/
	dels=sigmap*delx1;
	exps=exp(dels);
	sinhs=.5*(exps-1./exps);
	sinhin=1./(delx1*sinhs);
	diag1=sinhin*(dels*.5*(exps+1./exps)-sinhs);
	diagin=1./diag1;
	yp[0]=diagin*(dx1-slpp1);
	spdiag=sinhin*(sinhs-dels);
	temp[0]=diagin*spdiag;
	if(n!=2)
		{for(i=1; i<=n-2; i++)
			{delx2=x[i+1]-x[i];
			dx2=(y[i+1]-y[i])/delx2;
			dels=sigmap*delx2;
			exps=exp(dels);
			sinhs=.5*(exps-1./exps);
			sinhin=1./(delx2*sinhs);
			diag2=sinhin*(dels*(.5*(exps+1./exps))-sinhs);
			diagin=1./(diag1+diag2-spdiag*temp[i-1]);
			yp[i]=diagin*(dx2-dx1-spdiag*yp[i-1]);
			spdiag=sinhin*(sinhs-dels);
			temp[i]=diagin*spdiag;
			dx1=dx2;
			diag1=diag2;
			}
		}
	diagin=1./(diag1-spdiag*temp[n-2]);
	yp[n-1]=diagin*(slppn-dx2-spdiag*yp[n-2]);
					/* perform back substitution */
	for (i=n-2; i>=0; i--) yp[i] -= temp[i]*yp[i+1];
}


double curv2(x,y,yp,t,n) double *x,*y,*yp,t; int n;
{	int i,j;
	static int i1=1;
	double del1,del2,dels,exps,exps1,s,sigmap,sinhd1,sinhd2,sinhs;

	s=x[n-1]-x[0];
	sigmap=fabs(sigma)*(n-1)/s;
#ifdef WORK
	for (j=2; j; j--)	/* want: x[i-1] <= t < x[i], 0 < i <= n */
		{for (i=i1; i<n; i++)
			{if(x[i]>t) break;
			}
		if(i==n) i=n-1;
		if(x[i-1]<=t || t<=x[0]) break;
		i1=1;
		}
#endif
	i=i1;
	while(i<n && t>=x[i]) i++;
	while(i>1 && x[i-1]>t) i--;
	i1=i;
	del1=t-x[i-1];
	del2=x[i]-t;
	dels=x[i] - x[i-1];
	exps1=exp(sigmap*del1); sinhd1=.5*(exps1-1./exps1);
	exps= exp(sigmap*del2); sinhd2=.5*(exps-1./exps);
	exps=exps1*exps;        sinhs=.5*(exps-1./exps);
	return ((yp[i]*sinhd1 + yp[i-1]*sinhd2)/sinhs +
			((y[i] - yp[i])*del1 + (y[i-1] - yp[i-1])*del2)/dels);
}

double mylog(x) double x;
{	if(x>0.) return log(x);
	fprintf(stderr,"can%'t take log of nonpositive number");
	exit(1);
	return 0.;
}