========================================================
This is an advanced setting just for allowing increased choices to power users that have problems with a given sketch and want to
test different flavours of DogLeg algorithm.
This commit does not change the default behaviour of FreeCAD. It is only intended to give more options to power users.
The advanced solver configuration is extended to support three different Gauss-newton steps for DogLeg:
FullPivLU => h_gn = Jx.fullPivLu().solve(-fx);
LeastNormFullPivLU => h_gn = Jx.adjoint()*(Jx*Jx.adjoint()).fullPivLu().solve(-fx);
LeastNormLdlt => h_gn = Jx.adjoint()*(Jx*Jx.adjoint()).ldlt().solve(-fx);
This setting is applied only to DogLeg. It is applied to DogLeg as normal or redundant solver, if DogLeg is the selected solver.
Selecting a solver different from DogLeg for both normal and redundant disables the setting.
We have been told:
https://forum.kde.org/viewtopic.php?f=74&t=129439#p346104
that our default Gauss-Newton step in DogLeg may not be adequate in general (we generally deal with underconstraint systems
unless we have a fully constraint sketch, and even then it is many times overconstraint at least for redundant solving).
We have been told that maybe these LeastNorm options are more suitable for us (performance set aside). This enables you as power
user to test if it works fine with FreeCAD.
================================================================
A new parameter added to the form in order to control how low a value should be
to be considered zero (how high a value shall be to be accounted for in rank calculation)
Debug for QR pivot threshold is also added.
===============================================
- Increased solver debug
- Changing default values from float to string, as float has "only" a precision of 12 decimals.
- Default values as macros
==================================================================================
The solver has been adapted to use Eigen's SparseQR QR decomposition algorithm. The original
Dense QR implementation is maintained and can be selected using the Advanced Control TaskBox (see below).
The use of SparseQR provides over an order of magnitude improvement in solving time in complex sketches due to
the Sparse nature of the Jacobian matrix of the system of equations.
The solver advanced control is a new TaskBox in the Sketcher that allows to select which algorithms are to be used for
the different solving operations and tweak its parameters. It is not intended to be a user control, but means to debug
solving problems and improve the algorithms and their configuration.
This commit also introduces multithread support for Eigen. Currently it is only limited to products and does not provide
a substantial speed improvement. It is expected to have more multithreaded operations in Eigen in the future.
As a bonus, the TaskBoxes in the Taskbar of the Sketcher remember the last state (collapsed or deployed).
