51 lines
1.1 KiB
C++
51 lines
1.1 KiB
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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DP NR::zriddr(DP func(const DP), const DP x1, const DP x2, const DP xacc)
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{
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const int MAXIT=60;
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const DP UNUSED=-1.11e30;
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int j;
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DP ans,fh,fl,fm,fnew,s,xh,xl,xm,xnew;
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fl=func(x1);
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fh=func(x2);
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if ((fl > 0.0 && fh < 0.0) || (fl < 0.0 && fh > 0.0)) {
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xl=x1;
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xh=x2;
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ans=UNUSED;
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for (j=0;j<MAXIT;j++) {
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xm=0.5*(xl+xh);
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fm=func(xm);
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s=sqrt(fm*fm-fl*fh);
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if (s == 0.0) return ans;
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xnew=xm+(xm-xl)*((fl >= fh ? 1.0 : -1.0)*fm/s);
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if (fabs(xnew-ans) <= xacc) return ans;
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ans=xnew;
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fnew=func(ans);
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if (fnew == 0.0) return ans;
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if (SIGN(fm,fnew) != fm) {
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xl=xm;
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fl=fm;
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xh=ans;
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fh=fnew;
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} else if (SIGN(fl,fnew) != fl) {
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xh=ans;
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fh=fnew;
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} else if (SIGN(fh,fnew) != fh) {
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xl=ans;
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fl=fnew;
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} else nrerror("never get here.");
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if (fabs(xh-xl) <= xacc) return ans;
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}
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nrerror("zriddr exceed maximum iterations");
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}
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else {
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if (fl == 0.0) return x1;
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if (fh == 0.0) return x2;
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nrerror("root must be bracketed in zriddr.");
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}
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return 0.0;
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}
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