invMat

void SLAE::LUdecomposition()
{
    L.resize(eqcount);
    U.resize(eqcount);
    for (int i(0); i < eqcount; ++i) {
        L[i].resize(varcount);
        U[i].resize(varcount);
    }

    for (int i(0); i < eqcount; ++i) {
        for (int j(0); j < varcount; ++j) {
            if (i <= j) {
                U[i][j] = A[i][j];
                for (int t(0); t <= i; ++t) {
                    U[i][j] -= L[i][t] * U[t][j];
                }
            }
            else {
                L[i][j] = A[i][j];
                for (int t(0); t < j; ++t) {
                    L[i][j] -= L[i][t] * U[t][j];
                }
                L[i][j] /= U[j][j];
            }
        }
        L[i][i] = 1;
    }
}

void SLAE::LUsolution()
{
    LUdecomposition();
    std::vector<double> y(varcount);
    for (int j(0); j < varcount; ++j) {
        y[j] = B[j];
        for (int i(0); i < j; ++i) {
            y[j] -= L[j][i] * y[i];
        }
    }

    for (int j(eqcount - 1); j >= 0; --j) {
        solution[j] = y[j];
        for (int i(j + 1); i < varcount; ++i) {
            solution[j] -= U[j][i] * solution[i];
        }
        solution[j] /= U[j][j];
    }
}

std::vector<std::vector<double> > SLAE::inverseMatrix()
{
    LUdecomposition();
    std::vector<std::vector<double> > inv;
    inv.resize(eqcount);
    for (int i(0); i < eqcount; ++i) {
        inv[i].resize(varcount);
    }

    std::vector<double> b;
    for (int i(0); i < eqcount; ++i) {
        b.clear();
        for (int j(0); j < eqcount; ++j) {
            if (j == i) {
                b.push_back(1);
            }
            else {
                b.push_back(0);
            }
        }
        SLAE s(A, b);
        s.LUsolution();
        for (int j(0); j < eqcount; ++j) {
            inv[j][i] = s.solution[j];
        }
    }
    return inv;
}

void SLAE::invMatMethod()
{
    std::vector < std::vector<double> > invA(inverseMatrix());
    solution = invA * B;
}

//кусочек из мэйна
S.invMatMethod();
cout << "Solution:" << endl;
for (int i(0); i < n; ++i) {
    cout << "x" << i + 1 << " = " << S.solution[i] << endl;
}