Simple 3x3 matrix inverse code (C++)

Question

What\'s the easiest way to compute a 3x3 matrix inverse?

I\'m just looking for a short code snippet that\'ll do the trick for non-singular matrices, possibly using C

Answer 1

#include <iostream>
using namespace std;

int main()
{
    double A11, A12, A13;
    double A21, A22, A23;
    double A31, A32, A33;

    double B11, B12, B13;
    double B21, B22, B23;
    double B31, B32, B33;

    cout << "Enter all number from left to right, from top to bottom, and press enter after every number: ";
    cin  >> A11;
    cin  >> A12;
    cin  >> A13;
    cin  >> A21;
    cin  >> A22;
    cin  >> A23;
    cin  >> A31;
    cin  >> A32;
    cin  >> A33;

    B11 = 1 / ((A22 * A33) - (A23 * A32));
    B12 = 1 / ((A13 * A32) - (A12 * A33));
    B13 = 1 / ((A12 * A23) - (A13 * A22));
    B21 = 1 / ((A23 * A31) - (A21 * A33));
    B22 = 1 / ((A11 * A33) - (A13 * A31));
    B23 = 1 / ((A13 * A21) - (A11 * A23));
    B31 = 1 / ((A21 * A32) - (A22 * A31));
    B32 = 1 / ((A12 * A31) - (A11 * A32));
    B33 = 1 / ((A11 * A22) - (A12 * A21));

    cout << B11 << "\t" << B12 << "\t" << B13 << endl;
    cout << B21 << "\t" << B22 << "\t" << B23 << endl;
    cout << B31 << "\t" << B32 << "\t" << B33 << endl;

    return 0;
}