Hi there.
I wonder if anyone can help me.
I have this code but it only works for a 3 by 3 matrix. I was wondering if anyone could help me change it to a for loop so you can work out different matrixes like a 4 by 30 matrix.
#include <iostream>
#include <cmath>
using namespace std;
void gauss(int N, // number of unknowns
float A [20] [21], // coefficients and constants
float result[20],
bool& err)
// Solve system of N linear equations with N unknowns
// using Gaussian elimination with scaled partial pivoting
// First N rows and N+1 columns of A contain the system
// with right-hand sides of equations in column N+1
// err returns true if process fails; false if it is successful
// original contents of A are destroyed
// solution appears in column N
{
int indx[20];
float scale[20];
float maxRatio;
int maxIndx;
int tmpIndx;
float ratio;
float sum;
for (int i = 0; i < N; i++) indx = i; // index array initialization
// determine scale factors
for (int row = 0; row < N; row++)
{
scale[row] = abs(A[row][0]);
for (int col = 1; col < N; col++)
{
if (abs(A[row][col]) > scale[row]) scale[row] = abs(A[row][col]);
}
}
// forward elimination
for (int k = 0; k < N; k++)
{
// determine index of pivot row
maxRatio = abs(A[indx[k]] [k])/scale[indx[k]];
maxIndx = k;
for (int i = k+1; i < N; i++)
{
if (abs(A[indx] [k])/scale[indx] > maxRatio)
{
maxRatio = abs(A[indx] [k])/scale[indx];
maxIndx = i;
}
}
if (maxRatio == 0) // no pivot available
{
err = true;
return;
}
tmpIndx =indx[k]; indx[k]=indx[maxIndx]; indx[maxIndx] = tmpIndx;
// use pivot row to eliminate kth variable in "lower" rows
for (int i = k+1; i < N; i++)
{
ratio = -A[indx] [k]/A[indx[k]] [k];
for (int col = k; col <= N; col++)
{
A[indx] [col] += ratio*A[indx[k]] [col];
}
}
}
// back substitution
for (int k = N-1; k >= 0; k--)
{
sum = 0;
for (int col = k+1; col < N; col++)
{
sum += A[indx[k]] [col] * A[indx[col]] [N];
}
A[indx[k]] [N] = (A[indx[k]] [N] - sum)/A[indx[k]] [k];
}
for (int k = 0; k < N; k++) result[k] = A[indx[k]] [N];
}
int main()
{
float A[20][21];
float X[20];
bool err;
int N;
float x1,x2,x3,y1,y2,y3,z1,z2,z3,b1,b2,b3;
cout << "Enter X1: ";
cin>> x1;
A[0][0] = x1;
cout << "Enter Y1: ";
cin>> y1;
A[0][1] = y1;
cout << "Enter Z1: ";
cin>> z1;
A[0][2] = z1;
cout << "Enter B1: ";
cin>> b1;
A[0][3] = b1;
//----------
cout << "Enter X2: ";
cin>> x2;
A[1][0] = x2;
cout << "Enter Y2: ";
cin>> y2;
A[1][1] = y2;
cout << "Enter Z2: ";
cin>> z2;
A[1][2] = z2;
cout << "Enter B2: ";
cin>> b2;
A[1][3] = b2;
//-----------
cout << "Enter X3: ";
cin>> x3;
A[2][0] = x3;
cout << "Enter Y3: ";
cin>> y3;
A[2][1] = y3;
cout << "Enter Z3: ";
cin>> z3;
A[2][2] = z3;
cout << "Enter B3: ";
cin>> b3;
A[2][3] = b3;
gauss(3, A, X, err);
for (int i=0; i<3; i++) cout << X << " ";
std::cin.get();
return 0;
}
