Jacobi c++

[mimito]

Where is my mistake? Please help , it only do the first iteration.

#include <iostream>
#include <cstring>
#include <cmath>
using namespace std;

const int p=1;
int main()
{
    int n=2;

   float A[n][n];
    for(int i=0;i<=n;i++)
       { for(int j=0;j<=n;j++)
    {
        cout<<"A["<<i<<"]["<<j<<"]: ";
        cin>>A[i][j];
    }
    }

    double b[n];
    cout<<"b: "<<endl;
    for(int i=0;i<=n;i++)
    {
        cout<<"b["<<i<<"] : ";
        cin>>b[i];
    }
    cout<<endl;

    float c[n][n];
    for(int i=0;i<=n;i++)
    {   for(int j=0;j<=n;j++)
    {
         c[i][j]= -(A[i][j]/A[i][i]);
    }
             c[i][i]=0;
    }

    float d[n];
    for(int i=0;i<=n;i++)
    {
        d[i]=b[i]/A[i][i];
    }

    cout<<"d= "<<endl;
    for(int i=0;i<=n;i++)
    {
        cout<<d[i]<<endl;
    }
    cout<<endl;
        float x[n];
        float xnew[n];
        for(int i=0;i<=n;i++)
        {
            x[i]=0;
            cout<<"x["<<i<<"]="<<x[i]<<'\t';
            xnew[i]=0;
        }
        cout<<endl;
        for(int k=0;k<=p;k++)
       { for(int i=0;i<=n;i++)
        {
            xnew[i]=d[i];
            for(int j=0;j<=n;j++)
            {
                if(i!=j)
                {
                    xnew[i]+=c[i][j]*x[i];
                }
            }
            x[i]=xnew[i];
            cout<<"x["<<i<<"]= "<<x[i]<<'\t';
        }
         cout<<endl;
       }
    return 0;
}

[cire]

Valid indices for an array are 0 to size-1 where size is the number of elements in the array.

You access outside the bounds of the array(s) resulting in undefined behavior. Don't access outside the bounds of the array(s.)

[mimito]

So what should I change?

[wildblue]

If you have an array with 2 elements, the indices of those elements will be 0 and 1. If you run your for loop from 0 to <=2, then you will be trying to access indices 0, 1 and 2. If you want to stay in bounds, the for loop should just run from 0 to 1 (i.e. <2).

In general, that's 0 to size-1 as cire pointed out, where size is the number of elements in the array.

[mimito]

Oh my bad .. n=2 because of the arrays .. I need the arrays to be with 3 elements , thats why in the for loops i have <=

[mimito]

anyone ?

[coder777]

If you want 3 elements then make

const int n=3; // Note: const otherwise it's invalid [current] C++

and what the other say:

for(int i=0;i<n;i++) // Note: < not <=

[mimito]

Ok , but it still doesn't work

[LB]

What exactly does "doesn't work" mean? Does it distribute illegal content? Does it randomly mute your volume or turn it to max? Does it cause inflation in a foreign country? You need to be specific.

[mimito]

Sorry,
Well , it finds the first iteration correctly, but the second and further aren't correct ..

[mimito]

:(

[mimito]

help please :(

[mimito]

:(

[wildblue]

If I put the changes coder777 suggested into your code and input random numbers (1 through 18 for A, and 22,23,24 for B), I get this output. What output are you expecting if this isn't what you wanted?

A[0][0]: A[0][1]: A[0][2]: A[1][0]: A[1][1]: A[1][2]: A[2][0]: A[2][1]: A[2][2]: b: 
b[0] : b[1] : b[2] : 
d= 
10
2.2
1.33333

x[0]=0	x[1]=0	x[2]=0	
x[0]= 10	x[1]= 2.2	x[2]= 1.33333	
x[0]= -40	x[1]= -2.2	x[2]= -0.888889	

[mimito]

http://math.semestr.ru/optim/iter.php here is the online calculator for this :)