Re: [eigen] Mapping array of scalars into quaternions

[Mathieu Gautier <mathieu.gautier@xxxxxx>]

Hi,

> typedef Quaternion<MyScalar> MyQuat;
>
> and not:
>
> typedef Quaternion<Matrix<MyScalar,4,1> > MyQuat;
>
> right ?

Yes, I want to keep the former Quaternion notation.

> then the first template argument of Quaternion must be the scalar type. 
> But if we prefer we can also introduce a QuaternionBase and a 
> QuaternionWrapper classes like we did for DiagonalMatrix. Of course this 
> is more work, but perhaps that's a good idea to harmonize that over Eigen.

Besides quaternions, i want to have two distinct members of Lie algebras 
which represent angular velocities of a rigid body or torques applied on 
a rigid body which could be represented by vectors of 3 elements. I need 
to have a Lie bracket [A,B] = AB - BA which had a specific 
implementation for thoses vectors. Moreover, I need a map mecanism to 
interface Eigen with an another library.

So, I have severals options :

1) Add this function in MatrixBase (through the plugin mecanism) whith 
some asserts to check that the function is called only on vectors.

2) Do something similar to the actual Quaternion class with (a proper 
version of) my patch.

3) Inherit a new class (FooBase) from MatrixBase and introduce two other 
classes Foo and FooWrapper.

Since, these new objects are vectors (like quaternions in fact), the 1st 
and 2nd options would benefit from the map mecanism of matrices.

The 3rd option looks like what we actually have in our own libraries 
that could reduce my work to adapt our algorithms to Eigen.

So, I wonder which option to choose in regards with your opinion on 
Wrapper and map mecanisms.

--
Mathieu Gautier