33 lines
598 B
C
33 lines
598 B
C
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#include "nrutil.h"
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void rk4(y,dydx,n,x,h,yout,derivs)
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float dydx[],h,x,y[],yout[];
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int n;
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void (*derivs)();
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{
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int i;
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float xh,hh,h6,*dym,*dyt,*yt;
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dym=vector(1,n);
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dyt=vector(1,n);
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yt=vector(1,n);
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hh=h*0.5;
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h6=h/6.0;
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xh=x+hh;
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for (i=1;i<=n;i++) yt[i]=y[i]+hh*dydx[i];
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(*derivs)(xh,yt,dyt);
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for (i=1;i<=n;i++) yt[i]=y[i]+hh*dyt[i];
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(*derivs)(xh,yt,dym);
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for (i=1;i<=n;i++) {
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yt[i]=y[i]+h*dym[i];
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dym[i] += dyt[i];
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}
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(*derivs)(x+h,yt,dyt);
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for (i=1;i<=n;i++)
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yout[i]=y[i]+h6*(dydx[i]+dyt[i]+2.0*dym[i]);
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free_vector(yt,1,n);
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free_vector(dyt,1,n);
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free_vector(dym,1,n);
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}
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