49 lines
947 B
C
49 lines
947 B
C
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/* Driver for routine rk4 */
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#include <stdio.h>
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#define NRANSI
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#include "nr.h"
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#include "nrutil.h"
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#define N 4
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void derivs(float x,float y[],float dydx[])
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{
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dydx[1] = -y[2];
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dydx[2]=y[1]-(1.0/x)*y[2];
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dydx[3]=y[2]-(2.0/x)*y[3];
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dydx[4]=y[3]-(3.0/x)*y[4];
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}
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int main(void)
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{
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int i,j;
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float h,x=1.0,*y,*dydx,*yout;
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y=vector(1,N);
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dydx=vector(1,N);
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yout=vector(1,N);
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y[1]=bessj0(x);
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y[2]=bessj1(x);
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y[3]=bessj(2,x);
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y[4]=bessj(3,x);
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derivs(x,y,dydx);
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printf("\n%16s %5s %12s %12s %12s\n",
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"Bessel function:","j0","j1","j3","j4");
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for (i=1;i<=5;i++) {
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h=0.2*i;
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rk4(y,dydx,N,x,h,yout,derivs);
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printf("\nfor a step size of: %6.2f\n",h);
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printf("%12s","rk4:");
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for (j=1;j<=4;j++) printf(" %12.6f",yout[j]);
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printf("\n%12s %12.6f %12.6f %12.6f %12.6f\n","actual:",
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bessj0(x+h),bessj1(x+h),bessj(2,x+h),bessj(3,x+h));
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}
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free_vector(yout,1,N);
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free_vector(dydx,1,N);
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free_vector(y,1,N);
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return 0;
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}
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#undef NRANSI
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