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Numerical Methods c++

mimito (17)
Hello everyone ,
I am new in C++ . I have a homework to do .
Can anyone help me with doing a program for cubic spline interpolation , with given first derivative ?


Thank you
helios (17574)
Do you have any specific questions?
mimito (17)
Well ,not really.
I can't do it . I don't know how to make it , how to make the matrix
I will be thankful if someone sent me a code if he/she done this before , or try to help me



PLease help mee :( !
Last edited on
mimito (17)
Anyone ? :(
mimito (17)
i have done this ..

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#include <math.h>

#include <iostream>
using namespace std;
void ccspline(int n, long double *x, long double *a, long double FPO, long double FPN)

{

long double *b, *c, *d, *h, *e, *z, *u, *l;

b= new long double[n+1];

c= new long double[n+1];

d= new long double[n+1];

h= new long double[n+1];

e= new long double[n+1];

z= new long double[n+1];

u= new long double[n+1];

l= new long double[n+1];

int i;

for (i=0;i<n;i++)

h[i]=x[i+1]-x[i];

e[0]=3*(a[1]-a[0])/h[0]-3*FPO;

e[n]=3*FPN-3*(a[n]-a[n-1])/h[n-1];

for (i=1;i<n;i++)

e[i]=3/h[i]*(a[i+1]-a[i])-3/h[i-1]*(a[i]-a[i-1]);

l[0]=2*h[0];

u[0]=0.5;

z[0]=e[0]/l[0];

for(i=1;i<n;i++)

{

l[i]=2*(x[i+1]-x[i-1]) - h[i-1]*u[i-1];

u[i] = h[i]/l[i];

z[i] = ( e[i]-h[i-1]*z[i-1])/l[i];

};

l[n]=h[n-1]*(2-u[n-1]);

z[n]=(e[n]-h[n-1]*z[n-1])/l[n];

c[n]=z[n];

for(i=n-1;i>=0;i--)

{

c[i]=z[i]-u[i]*c[i+1];

b[i]=(a[i+1]-a[i])/h[i]-h[i]*(c[i+1]+2*c[i])/3;

d[i]=(c[i+1]-c[i])/(3*h[i]);

};

for(i=0; i<n;i++)

cout << a[i] << ", " << b[i]<<", "<<c[i]<<", "<<d[i]<<endl;

};

int main()

{

int n,i;

long double *a,*x,FPO,FPN;

cout << " How many intervals?" ;

cin >> n;

a=new long double[n+1];

x=new long double[n+1];

cout << endl << " Input the x coords: " << endl;

for (i=0;i<n+1;i++)

cin >> x[i];

cout << endl << " thanks, now the f(x)'s " << endl;

for (i=0;i<n+1;i++)

cin >> a[i];

cout << endl<< " Enter f'(x0) and f'(xn) please " << endl;

cin >> FPO;

cin >> FPN;

cout << " The spline follows " << endl;

ccspline(n,x,a,FPO,FPN);

};



but when i have
x[i] = 3 ; 4,5 ; 7 ;9
f[i]= 2.5 ; 1 ; 2.5 ; 0.5
f'(xo) = 0
f'(xn)= 0
i get for the coefficients :
s1: 2.5 ; 0; -1.63913 ; 0.648309
s2 : 1 ; -0.541304 ; 1.27826 ; -0.328696
s3 : 2.5 ; -0.313043 ; -1.18696 ; 0.421739

but it should be :
s1: 2.5 , 0 , -1,4198 , 0,1866
s2 : 1 , -0,1605 , 0.8395 , -0.2141
s3 : 2.5 , 0.0221 , -0.7666 , 0.1278
mimito (17)
Can someone help me please :( ?
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