Re: [eigen] writing a function that takes Eigen::MatrixBase or Eigen::Block

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 04/10/2019 15.53, Dale Lukas Peterson wrote:
> [...]
>
> I ended up doing this as:
> Eigen::Matrix<typename Derived::Scalar, Derived::RowsAtCompileTime,
> Derived::ColsAtCompileTime> aa;
>
> However I like your solution better since it is shorter and presumably it
> also captures the Options, MaxRows, and MaxCols template parameters
> correctly from Derived, whereas what I did will use whatever the defaults
> are configured to be.

Yes, `typename Derived::PlainObject` will also copy 
`MaxRowsAtCompileTime` and `MaxColsAtCompileTime`. However, from the 
Options it will only take the Majornes (RowMajor or ColumnMajor) but 
always use `AutoAlign`. In your case the default values are the same.

Also, if you used `DenseBase<Derived>` instead of `MatrixBase<Derived>` 
it would automatically choose either the corresponding Matrix or Array 
class. If you explicitly want a Matrix (or an Array) you could use 
`Derived::PlainMatrix` (or `Derived::PlainArray`).


Christoph




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