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add numerical recipes library

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yenru0
2025-09-12 18:55:25 +09:00
parent d4dff245bd
commit 2c75620ec9
1344 changed files with 63869 additions and 0 deletions
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32
lib/nr/k_and_r/recipes/rk4.c Normal file
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#include "nrutil.h"
void rk4(y,dydx,n,x,h,yout,derivs)
float dydx[],h,x,y[],yout[];
int n;
void (*derivs)();
{
int i;
float xh,hh,h6,*dym,*dyt,*yt;
dym=vector(1,n);
dyt=vector(1,n);
yt=vector(1,n);
hh=h*0.5;
h6=h/6.0;
xh=x+hh;
for (i=1;i<=n;i++) yt[i]=y[i]+hh*dydx[i];
(*derivs)(xh,yt,dyt);
for (i=1;i<=n;i++) yt[i]=y[i]+hh*dyt[i];
(*derivs)(xh,yt,dym);
for (i=1;i<=n;i++) {
yt[i]=y[i]+h*dym[i];
dym[i] += dyt[i];
}
(*derivs)(x+h,yt,dyt);
for (i=1;i<=n;i++)
yout[i]=y[i]+h6*(dydx[i]+dyt[i]+2.0*dym[i]);
free_vector(yt,1,n);
free_vector(dyt,1,n);
free_vector(dym,1,n);
}