54 lines
1.1 KiB
C
54 lines
1.1 KiB
C
|
|
#include <math.h>
|
|
#include "nrutil.h"
|
|
#define MAXIT 60
|
|
#define UNUSED (-1.11e30)
|
|
|
|
float zriddr(func,x1,x2,xacc)
|
|
float (*func)(),x1,x2,xacc;
|
|
{
|
|
int j;
|
|
float ans,fh,fl,fm,fnew,s,xh,xl,xm,xnew;
|
|
|
|
fl=(*func)(x1);
|
|
fh=(*func)(x2);
|
|
if ((fl > 0.0 && fh < 0.0) || (fl < 0.0 && fh > 0.0)) {
|
|
xl=x1;
|
|
xh=x2;
|
|
ans=UNUSED;
|
|
for (j=1;j<=MAXIT;j++) {
|
|
xm=0.5*(xl+xh);
|
|
fm=(*func)(xm);
|
|
s=sqrt(fm*fm-fl*fh);
|
|
if (s == 0.0) return ans;
|
|
xnew=xm+(xm-xl)*((fl >= fh ? 1.0 : -1.0)*fm/s);
|
|
if (fabs(xnew-ans) <= xacc) return ans;
|
|
ans=xnew;
|
|
fnew=(*func)(ans);
|
|
if (fnew == 0.0) return ans;
|
|
if (SIGN(fm,fnew) != fm) {
|
|
xl=xm;
|
|
fl=fm;
|
|
xh=ans;
|
|
fh=fnew;
|
|
} else if (SIGN(fl,fnew) != fl) {
|
|
xh=ans;
|
|
fh=fnew;
|
|
} else if (SIGN(fh,fnew) != fh) {
|
|
xl=ans;
|
|
fl=fnew;
|
|
} else nrerror("never get here.");
|
|
if (fabs(xh-xl) <= xacc) return ans;
|
|
}
|
|
nrerror("zriddr exceed maximum iterations");
|
|
}
|
|
else {
|
|
if (fl == 0.0) return x1;
|
|
if (fh == 0.0) return x2;
|
|
nrerror("root must be bracketed in zriddr.");
|
|
}
|
|
return 0.0;
|
|
}
|
|
#undef MAXIT
|
|
#undef UNUSED
|