55 lines
1.0 KiB
C
55 lines
1.0 KiB
C
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#include <math.h>
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#define MAXIT 100
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float rtsafe(void (*funcd)(float, float *, float *), float x1, float x2,
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float xacc)
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{
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void nrerror(char error_text[]);
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int j;
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float df,dx,dxold,f,fh,fl;
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float temp,xh,xl,rts;
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(*funcd)(x1,&fl,&df);
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(*funcd)(x2,&fh,&df);
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if ((fl > 0.0 && fh > 0.0) || (fl < 0.0 && fh < 0.0))
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nrerror("Root must be bracketed in rtsafe");
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if (fl == 0.0) return x1;
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if (fh == 0.0) return x2;
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if (fl < 0.0) {
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xl=x1;
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xh=x2;
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} else {
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xh=x1;
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xl=x2;
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}
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rts=0.5*(x1+x2);
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dxold=fabs(x2-x1);
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dx=dxold;
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(*funcd)(rts,&f,&df);
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for (j=1;j<=MAXIT;j++) {
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if ((((rts-xh)*df-f)*((rts-xl)*df-f) > 0.0)
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|| (fabs(2.0*f) > fabs(dxold*df))) {
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dxold=dx;
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dx=0.5*(xh-xl);
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rts=xl+dx;
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if (xl == rts) return rts;
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} else {
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dxold=dx;
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dx=f/df;
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temp=rts;
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rts -= dx;
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if (temp == rts) return rts;
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}
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if (fabs(dx) < xacc) return rts;
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(*funcd)(rts,&f,&df);
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if (f < 0.0)
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xl=rts;
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else
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xh=rts;
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}
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nrerror("Maximum number of iterations exceeded in rtsafe");
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return 0.0;
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}
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#undef MAXIT
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