Is it possible to initialize a const Eigen matrix?

Question

I have the following class:

class Foo
{
public:
   Foo(double a, double b, double c, double d, double e)
   // This does not work:
   // : m_bar(a, b, c, d, e)
   {
      m_bar << a, b, c, d, e;
   }

private:
   // How can I make this const?
   Eigen::Matrix<double, 5, 1, Eigen::DontAlign> m_bar;
};

How Can I make m_bar const and initialize it width a to f as values in the constructor? C++11 would also be fine, but initializer lists don't seem to be supported by eigen...

Do you mean that library: http://eigen.tuxfamily.org? – Stefan Weiser Aug 06 '14 at 11:37 — Stefan Weiser, Aug 06 '14 at 11:37
Yes, exactly! Version 3.2.1 – Jan Rüegg Aug 06 '14 at 11:39 — Jan Rüegg, Aug 06 '14 at 11:39

Marco A. · Accepted Answer · 2014-08-06T11:55:18.347

14

Simplest solution I see since the class also defines a copy constructor:

class Foo
{
public:
   Foo(double a, double b, double c, double d, double e) :
       m_bar( (Eigen::Matrix<double, 5, 1, Eigen::DontAlign>() << a, b, c, d, e).finished() )
   {
   }

private:
   const Eigen::Matrix<double, 5, 1, Eigen::DontAlign> m_bar;
};

edited Aug 06 '14 at 11:55

answered Aug 06 '14 at 11:46

Marco A.

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Unfortunately, this doesn't work. I get the following error: no matching function for call to 'Eigen::Matrix::Matrix(Eigen::CommaInitializer >&)' – Jan Rüegg Aug 06 '14 at 11:49
@JanRüegg forgot the "finished" part, sorry – Marco A. Aug 06 '14 at 11:55
1

Does this copy the data? I get the impression that Eigen's hasn't fully implemented move yet. – Channing Moore Feb 04 '16 at 15:25

Jarod42 · Answer 2 · 2014-08-06T11:58:42.773

You may do a utility function

Eigen::Matrix<double, 5, 1, Eigen::DontAlign>
make_matrix(double a, double b, double c, double d, double e)
{
    Eigen::Matrix<double, 5, 1, Eigen::DontAlign> m;

    m << a, b, c, d, e;
    return m;
}

And then:

class Foo
{
public:
   Foo(double a, double b, double c, double d, double e) :
       m_bar(make_matrix(a, b, c, d, e))
   {
   }

private:
   const Eigen::Matrix<double, 5, 1, Eigen::DontAlign> m_bar;
};

Or you can inline that function and using finished() :

class Foo
{
    using MyMatrice = Eigen::Matrix<double, 5, 1, Eigen::DontAlign>;
public:
   Foo(double a, double b, double c, double d, double e) :
       m_bar((MyMatrice() << a, b, c, d, e).finished())
   {
   }

private:
   const MyMatrice m_bar;
};

In what file should you put the utility function? If you put it in the cpp file where the class is initialized, would it pollute the global namespace? — Lucas Myers, Jun 11 '21 at 16:37

Is it possible to initialize a const Eigen matrix?

2 Answers2