4 replies to this topic

[Sega]

Hello
Help to correct the program, defines roots correctly, but in a wrong order :sad:

#include <iostream>

#include <cmath>



using namespace std;


void Gauss(double *a, double *b, double *x,int n) {

 int i,j,k,t;

 double kof,s;

 double temp;

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

 {

  for (t=i, j=i-1; j>=0; --j) 

  {

   if (fabs(a[i*n+t])<fabs(a[i*n+j]))

   {

    t=j;

   }

  }

  if (a[i*n+t]==0.0)

  {

   return;

  }

  if (t!=i) 

  {

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

   {

    temp=a[k*n+t];

    a[k*n+t]=a[k*n+i];

    a[k*n+i]=temp;

   }

  }

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

  {

   kof=a[i+j*n]/a[i*n+i]; // kof=a[j][i]/a[i][i];

   for (a[i+j*n]=0.0, b[j]-=b[i]*kof, k=i-1; k>=0; --k) 

   {

    a[k+j*n]-=a[k+i*n]*kof; // a[k][j]-=a[k][i]*kof

   }

  }

 }

 x=new double [n];

 if (x)

 {

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

  {

   for (s=0.0, j=i-1; j>=0; --j)

   {

    s+=a[j+i*n]*x[j]; //s+=a[j][i]*x[j]

   }

   x[i]=(b[i]-s)/a[i*n+i]; // x[i]=(b[i]-s)/a[i][i];

   //cout << x[i] << "\n";

  }

 }

 cout << "\n";

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

cout << "x " << x[i] << endl;

}



main()

{


      int n = 6;

     double gauss2[6] ={1,5,3,7,6,3};

      double M[36]={-3, 2, 1,2, 3, 1,5, 3, 3, -1, 3, 4,0, 80,46, 34, 3, 4,6, 7, 3, 6, 6,7,57, 6, 5, 5, 3, 67,1, 55, 5, 7, 3, 7 };

        

      double *y = new double[n];


	/*  for(int i=0; i<n; i++)

		{

			for(int j=0; j<n; j++)

				{

					//cin >> M[i+j*n];

					 M[i+j*n] = rand()/100;

//cout << "gauss1["<< i << "][" << j << "]=";

//cin >> gauss1[i][j];

				}

		}

*/

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

		{

			for(int j=0; j<n; j++)

				{

					 cout << M[i*n+j] << "  ";

				}

				cout << gauss2[i] << endl;

		}	

      Gauss(M,gauss2,y,n);

       cin.get();

}

My answer: 0.63, -0.12, 0.0249, 1.16, -0.49, -0.0558
Right answer: 0.63, 0.06, 0.02, -0.12, 1.16, -0.49

[WingedPanther]

Why not just sort your array before outputting it? Gauss's method is not guaranteed to generate roots in any particular order.

[Sega]

WingedPanther said:

Gauss's method is not guaranteed to generate roots in any particular order.

Why does not guaranteed? In fact, after finding the roots, of their substitute in a certain order, and not in an arbitrary, is not it?

[Sega]

If Substituting: 0.63, -0.12, 0.0249, 1.16, -0.49, -0.0558 , then the right decision not succeed
so that the sequence of roots is important

[WingedPanther]

Again, why not just sort the array before printing it?