?? xspline.cpp
字號:
#include <iostream>
#include <iomanip>
#include <cmath>
#include "nr.h"
using namespace std;
// Driver for routine spline
int main(void)
{
const int N=20;
const DP PI=3.141592653589793238;
int i;
DP yp1,ypn;
Vec_DP x(N),y(N),y2(N);
cout << endl << "second-derivatives for sin(x) from 0 to pi" << endl;
// Generate array for interpolation
for (i=0;i<20;i++) {
x[i]=(i+1)*PI/N;
y[i]=sin(x[i]);
}
// calculate 2nd derivative with spline
yp1=cos(x[0]);
ypn=cos(x[N-1]);
NR::spline(x,y,yp1,ypn,y2);
// test result
cout << setw(23) << "spline" << setw(17) << "actual" << endl;
cout << setw(7) << "angle" << setw(19) << "2nd deriv";
cout << setw(17) << "2nd deriv" << endl;
cout << fixed << setprecision(6);
for (i=0;i<N;i++) {
cout << setw(9) << x[i] << setw(17) << y2[i];
cout << setw(17) << -sin(x[i]) << endl;
}
return 0;
}
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