eigen library in C++ gives error C2660: 'Eigen::MatrixBase<Derived>::eigenvalues' : function does not take 2 arguments

Question

#include <iostream>
#include <math.h>
#include <conio.h>
#include <time.h>
#include <stdlib.h>
#include <dense>
#include <Eigenvalues> 

using namespace Eigen;
using namespace std;

void main()
{
    int i, j;
    float S = 2.5, g = 1, B = 1, H = 1, D = 1, E = 1, G, Sz1, Sz2, Sz3, Sz4, Kp, Kpp, Km, Kmm, E1, E2;

    Sz1 = -S;
    Sz2 = -S;
    G = g * B * H;
    G = 1;

    MatrixXf Ham(6, 6);

    for (i = 1; i <= 2 * S + 1; i++)
    {
        Sz2 = -S;
        for (j = 1; j <= 2 * S + 1; j++)
        {
            E1 = 0;
            Kp = 0;
            E2 = 0;
            Kpp = 0;
            Km = 0;
            Kmm = 0;

            Sz3 = Sz2;
            Sz4 = Sz2;

            if (i == j)
            {
                Ham(i, j) = (G * Sz2) + D * (Sz2 * Sz2 - (1 / 3) * S * (S + 1));
            }
            else
            {
                Kp = sqrt(S * (S + 1) - Sz3 * (Sz3 + 1));
                Sz3 = Sz3 + 1;
                Kpp = sqrt(S * (S + 1) - Sz3 * (Sz3 + 1));
                Sz3 = Sz3 + 1;

                if (Sz3 == Sz1)
                {
                    E1 = Kp * Kpp;
                }
                else
                {
                    E1 = 0;
                }

                Km = sqrt(S * (S + 1) - Sz4 * (Sz4 - 1));
                Sz4 = Sz4 - 1;
                Kmm = sqrt(S * (S + 1) - Sz4 * (Sz4 - 1));
                Sz4 = Sz4 - 1;

                if (Sz4 == Sz1)
                {
                    E2 = Km * Kmm;
                }
                else
                {
                    E2 = 0;
                }
                Ham(i, j) = (E1 + E2) / 2;
            }
            Sz2 = Sz2 + 1;
        }
        Sz1 = Sz1 + 1;
    }

    VectorXf eivals = Ham.eigenvalues(6, 6);
    cout << "The eigenvalues of the Hamiltonian matrix are:" << endl << eivals << endl;

    system("pause");
}

When I want to compile this code, I get an error:

error C2660: 'Eigen::MatrixBase<Derived>::eigenvalues' : function does not take 2 arguments with

Derived = Eigen::Matrix<float, -1, -1>

Can anybody help me to fix this problem?

Answer 1

The code below compiles with g++ 4.7.3 under Ubuntu/Linaro with package libeigen3-dev and runs.

Problems in your code:

1. don't give arguments for eigenvalues
2. not index range 1...size but 0...size-1 (I corrected this by substituting Ham(i,j) by Ham(i-1,j-1)
3. return type of eigenvalues is VectorXcf and not VectorXf

---

#include <iostream>
#include <math.h>
// #include <conio.h>
#include <time.h>
#include <stdlib.h>
#include <eigen3/Eigen/Dense>
#include <eigen3/Eigen/Eigenvalues> 

using namespace Eigen;
using namespace std;

int main()
{
    int i, j;
    float S = 2.5, g = 1, B = 1, H = 1, D = 1, E = 1, G, Sz1, Sz2, Sz3, Sz4, Kp, Kpp, Km, Kmm, E1, E2;

    Sz1 = -S;
    Sz2 = -S;
    G = g * B * H;
    G = 1;

    MatrixXf Ham(6, 6);

    for (i = 1; i <= 2 * S + 1; i++)
    {
        Sz2 = -S;
        for (j = 1; j <= 2 * S + 1; j++)
        {
            E1 = 0;
            Kp = 0;
            E2 = 0;
            Kpp = 0;
            Km = 0;
            Kmm = 0;

            Sz3 = Sz2;
            Sz4 = Sz2;

            if (i == j)
            {
                Ham(i-1, j-1) = (G * Sz2) + D * (Sz2 * Sz2 - (1 / 3) * S * (S + 1));
            }
            else
            {
                Kp = sqrt(S * (S + 1) - Sz3 * (Sz3 + 1));
                Sz3 = Sz3 + 1;
                Kpp = sqrt(S * (S + 1) - Sz3 * (Sz3 + 1));
                Sz3 = Sz3 + 1;

                if (Sz3 == Sz1)
                {
                    E1 = Kp * Kpp;
                }
                else
                {
                    E1 = 0;
                }

                Km = sqrt(S * (S + 1) - Sz4 * (Sz4 - 1));
                Sz4 = Sz4 - 1;
                Kmm = sqrt(S * (S + 1) - Sz4 * (Sz4 - 1));
                Sz4 = Sz4 - 1;

                if (Sz4 == Sz1)
                {
                    E2 = Km * Kmm;
                }
                else
                {
                    E2 = 0;
                }
                Ham(i-1, j-1) = (E1 + E2) / 2;
            }
            Sz2 = Sz2 + 1;
        }
        Sz1 = Sz1 + 1;
    }

    VectorXcf eivals = Ham.eigenvalues();

    cout << "The eigenvalues of the Hamiltonian matrix are:" << endl << eivals << endl;



    system("pause");
}