Category : C Source Code
Archive : GRAFGEM1.ZIP
Filename : UTIL.C
Output of file : UTIL.C contained in archive : GRAFGEM1.ZIP
/*
* util.c
*
* some utlity functions for root polishing and evaluating
* polynomials.
*/
#include
#include
#include "solve.h"
/*
* evalpoly
*
* evaluate polynomial defined in coef returning its value.
*/
double
evalpoly (ord, coef, x)
int ord;
double *coef, x;
{
double *fp, f;
fp = &coef[ord];
f = *fp;
for (fp--; fp >= coef; fp--)
f = x * f + *fp;
return(f);
}
/*
* modrf
*
* uses the modified regula-falsi method to evaluate the root
* in interval [a,b] of the polynomial described in coef. The
* root is returned is returned in *val. The routine returns zero
* if it can't converge.
*/
int
modrf(ord, coef, a, b, val)
int ord;
double *coef;
double a, b, *val;
{
int its;
double fa, fb, x, lx, fx, lfx;
double *fp, *scoef, *ecoef;
scoef = coef;
ecoef = &coef[ord];
fb = fa = *ecoef;
for (fp = ecoef - 1; fp >= scoef; fp--) {
fa = a * fa + *fp;
fb = b * fb + *fp;
}
/*
* if there is no sign difference the method won't work
*/
if (fa * fb > 0.0)
return(0);
if (fabs(fa) < RELERROR) {
*val = a;
return(1);
}
if (fabs(fb) < RELERROR) {
*val = b;
return(1);
}
lfx = fa;
lx = a;
for (its = 0; its < MAXIT; its++) {
x = (fb * a - fa * b) / (fb - fa);
fx = *ecoef;
for (fp = ecoef - 1; fp >= scoef; fp--)
fx = x * fx + *fp;
if (fabs(x) > RELERROR) {
if (fabs(fx / x) < RELERROR) {
*val = x;
return(1);
}
} else if (fabs(fx) < RELERROR) {
*val = x;
return(1);
}
if ((fa * fx) < 0) {
b = x;
fb = fx;
if ((lfx * fx) > 0)
fa /= 2;
} else {
a = x;
fa = fx;
if ((lfx * fx) > 0)
fb /= 2;
}
lx = x;
lfx = fx;
}
fprintf(stderr, "modrf overflow %f %f %f\n", a, b, fx);
return(0);
}
Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!
This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.
But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/