[BUG] The constructor of DQ does not work for pure dual quaternions

[maripaf]

Bug description

• It should be possible to create a DQ object from an Eigen vector with the pure dual quaternion coefficients, that is, a vector of size 6.
  In fact, the library does not complain when creating a DQ from a vector of size 6. However, instead of creating a pure dual quaternion, it creates a DQ object with the first 6 elements equal to the elements of the vector, that is
  q(0) + q(1)i + q(2)j + q(3)k + E*(q(4) + q(5)i + 0j + 0k)
  instead of
  0 + q(0)i + q(1)j + q(2)k + E*(0 + q(3)i + q(4)j + q(5)k).

To Reproduce

Code

#include <iostream>
#include <Eigen/Dense>
#include <dqrobotics/DQ.h>
#include <iostream>

using namespace DQ_robotics;

int main()
{
    Eigen::VectorXd force(6);
    force << 1, 2, 3, 4, 5, 6;
    std::cout << DQ(force) << std::endl;
   return 0;
}

Output

1 2i 3j 4k +E( 5 6i 0j 0k )

Expected behavior

Expected output

0 1i 2j 3k +E( 0 4i 5j 6k )

Environment:

• OS: Ubuntu16.04
• dqrobotics version: 0.1.0

Additional context

• It works fine in MATLAB version.

[mmmarinho]

Fixed and tested in:
https://github.com/dqrobotics/cpp-examples/blob/7c750a87bb7e7ed389593b1aa0f85ca6b87db244/cmake/simple_tests/simple_tests.cpp#L29