So i have to write a c++ program for the Graeffe's square root method
I have am stuck here when i have this formula transform into c++ code, the formula is on the link
The code works particulary, the (elem[j-1]*elem[j+i]) doesn't work, it's beeing ignored and i don't know why... can any one help me?
http://latex.codecogs.com/gif.latex?A_{k}=a_{k}^{2}+2\sum_{s=1}^{k}(-1)^{s}a_{k-s}*a_{k+s},&space;k=0,....n

cout<<"How many elements?"<<endl;
    cin>>n;
    cout<<"Insert the elements:"<<endl;
    for(int i=0; i<n; i++)
    {
        cin>>elem;
[*]
[*]    }
[*]
[*]
[*]    C[0]=pow(elem[0],2);
[*]
[*]    for(int j=1; j<n; j++)
[*]    {
[*]        C[j]=pow(elem[j],2);
[*]
[*]            int i=1;
[*]            while((i+j)<=n-1&&(i<=j))
[*]            {
[*]
[*]                C[j]=C[j]+(-1)^i*2*(elem[j-1]*elem[j+i]);
[*]                i=i+1;
[*]
[*]            }
[*]
[*]
[*]            cout<<"C"<<j<<":"<<C[j]<<endl;
[*]
[*]    }




http://latex.codecogs.com/gif.latex...}^{k}(-1)^{s}a_{k-s}*a_{k+s},&space;k=0,....n

http://latex.codecogs.com/gif.latex...}^{k}(-1)^{s}a_{k-s}*a_{k+s},&space;k=0,....n

 

Please provide comments or descriptions for what the various parts of your code are supposed to do and what they are actually doing that is not what you expect.

 

I had to write the formula above in c++, that what it supposed to do..
but it's ignoring one part of the formula and i don't know why

 

One bit that is a problem is here: C[j]=C[j]+(-1)^i*2*(elem[j-1]*elem[j+i]);

The ^ doesn't raise a number to a power, it is a bitwise exclusive or operation. As it appears to be intended to switch back and forth from 1 and -1, you could put this expression in its place: ((i & 1) ? -1 : 1)

Also in this part of the expression: C[j]=C[j]+(-1)^i*2*(elem[j-1]*elem[j+i]); The latex formula you've given shows that it's multiplying Ak-s * Ak+s, however your expression appears to multiply Ak-1 * Ak+s (minus 1 instead of minus s, or 'i' in your code)

Try changing those two things and see if that works out.


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