|[eigen] Accepting different matrix type in the decompositions|
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- Subject: [eigen] Accepting different matrix type in the decompositions
- From: "ESCANDE Adrien 222264" <adrien.escande@xxxxxx>
- Date: Tue, 20 Jul 2010 09:52:11 +0200
- Thread-index: Acsn4HYQOUduQtyiTxOKjYIVXERvwg==
- Thread-topic: Accepting different matrix type in the decompositions
the different decompositions (QR, LU...) I looked at are all templated by a type MatrixType and have, among others, a method compute(const MatrixType& matrix) with a line m_matrix = matrix, and a constructor
Decomposition(const MatrixType& matrix) calling compute.
I think it wouldn't hurt to template these two methods by a type InputMatrixName:
Decomposition<MatrixType>::Decomposition(const InputMatrixType& matrix)
Decomposition<MatrixType>::compute(const InputMatrixType& matrix)
this way, when InputMatrixType is different from MatrixType, there is no need to create a temporary object for the conversion, and this conversion is only made at the line m_matrix = matrix.
In the usual case where the user use the .decomposition() method of MatrixBase<Derived> (for example matrix.colPivHouseholderQR()), we have MatrixType = Derived::PlainObject and InputMatrixBase = Derived, and there's no need to call eval() within decomposition.
And this simplify the writing in other cases. My use case (a complete orthogonal decomposition):
HouseholderQR<MatrixXd> qr(LQ.matrixQR().topLeftCorner(LQ.rank(), LQ.cols()).triangularView<Upper>().transpose());
I don't even want to imagine the MatrixType I should have wrote for the HouseholderQR...
By adding the InputMatrixType template, I avoid there two temporaries.
I wanted to add a static assert to check for the compatibility of MatrixType and InputMatrixType, but ei_is_same_type<MatrixType, InputMatrixType::PlainObject>::ret seems to be a too strict condition. I just test the same scalar type for now.