Add LeastSquareCG-Solver from Eigen
This MR implements the LeastSquareCG Linear Solver from Eigen. With this solver rectangular (unsquare) equations systems (currently only in the HEAT_TRANSPORT_BHE) can be solved directly without forming the normalized equation A^T \cdot A \cdot x = A^T \cdot b, which results in a more accurate, faster and more stable solution. Additionally a bool can_solve_rectangular
is added to determine, if the solver can handle rectangular equation systems. If this bool is false, the normalization is furthermore performed for rectangular equation systems - but I added a warning.
For PETSC and Eigen the bool can_solve_rectangular
is set according to the specific solver. For the lis-solvers can_solve_rectangular
is always set to false, because I did not found specific information in the lis solver user guide about the possibility to solve rectangular equation systems.
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Feature description was added to the changelog -
Tests covering your feature were added? -
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