How to create a const boost matrix?

Question

How can I create a const boost matrix?

The following did not work:

const boost::numeric::ublas::matrix<double> arrayM(1, 3) = { {1.0, 2.0, 3.0} };

It doesn't work because you're declaring a const matrix and then attempting to assign values to it using a mutable assignment operator. GMan's solution below will do what you need. — Dan Story
– Dan Story, Commented Apr 2, 2010 at 22:48
I should have been clear about my question: Is there a way to create it in a similar way we create a const array? For example: int billy [5] = { 16, 2, 77, 40, 12071 }; — Journey Man
– Journey Man, Commented Apr 2, 2010 at 22:51

GManNickG · Accepted Answer · 2010-04-02 23:15:19Z

8

Usually something akin to:

typedef boost::numeric::ublas::matrix<double> matrix_type;

const matrix_type get_matrix(void)
{
    matrix_type result(1, 3);
    result(0, 0) = 1;
    result(0, 1) = 2;
    result(0, 2) = 3;

    return result;
}

const matrix_type arrayM = get_matrix();

You might also try something like this (mostly untested):

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>

template <typename T, typename L = boost::numeric::ublas::row_major,
            typename A = boost::numeric::ublas::unbounded_array<T> >
class matrix_builder
{
public:
    // types
    typedef boost::numeric::ublas::matrix<T, L, A> matrix_type;
    typedef typename matrix_type::size_type size_type;

    // creation
    matrix_builder(size_type pRows, size_type pColumns) :
    mMatrix(pRows, pColumns),
    mRow(0),
    mColumn(0)
    {}

    matrix_builder& operator()(const T& pValue)
    {
        mMatrix(mRow, mColumn) = pValue;
        if (++mColumn == mMatrix.size2())
        {
            mColumn = 0;
            mRow++;
        }

        return *this;
    }

    // access
    operator const matrix_type&(void) const
    {
        return mMatrix;
    }

private:
    // non copyable
    matrix_builder(const matrix_builder&);
    matrix_builder& operator=(const matrix_builder&);

    // members
    matrix_type mMatrix;
    size_type mRow;
    size_type mColumn;
};

typedef boost::numeric::ublas::matrix<double> matrix_type;

static const matrix_type m1 = matrix_builder<double>(3, 1)
                                (1)(2)(3);

static const matrix_type m2 = matrix_builder<double>(3, 3)
                                (1)(2)(3)
                                (4)(5)(6)
                                (7)(8)(9);

int main(void)
{
    std::cout << m1 << std::endl;
    std::cout << m2 << std::endl;
}

Same idea, more generic. Also a bit more visual, which can be nice.

edited Apr 2, 2010 at 23:15

answered Apr 2, 2010 at 22:46

GManNickG

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3 Comments

Journey Man Over a year ago

Though this works, I will have tor create a function for every const matrix type I need to create.

GManNickG Over a year ago

@Venkata: I'll write a more generic way now.

GManNickG Over a year ago

@Stacked: Thanks. I admit it could probably be done a bit better, but this should work for any case I can think of.

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