Enrichment of sparse-solvers, improved Multi-grid support (incl. hierarchical splines) #839

hverhelst · 2025-10-21T13:24:08Z

Improved support for preconditioners and multigrid:

Add gsSparseSolver<>::CGCustom, which is an Eigen iterative solver of which we can set the preconditioner from a gsPreconditioner. It is implemented via the gsPreconditionerWrapper, which wraps a gsPreconditioner into a format supported by Eigen.

typename gsSparseSolver<>::CGCustom solver;
solver.preconditioner().set(makeJacobiOp(mat));

Add solveWithGuess interface to Eigen's IterativeSolverBase solvers
Add gsGridHierarchy methods for hierarchical splines
Make the transfer matrix for gsHSplines a RowMajor by default. This is the format which is also used inside the grid hierarchy for Multi-Grid.
Add XML support for RowMajor sparse matrices

NEW:
Hierarchical spline support in gsGridHierarchy.
Add refineToLevel, refineCoarsestLevel, unrefineToLevel and unrefineFinestLevel to gsHTensorBasis

IMPROVED:
Template specialization for Gauss-Seidel preconditioner
Add more constructors to gsDofMapper, and make all mapper methods in gsMultiBasis and gsFeSpace use these constructors

Have you added an explanation of what your changes do and why
you'd like us to include them?
Have you documented any new codes using Doxygen comments?
Have you written new tests or examples for your changes?

- Functions for refinement and coarsening of finer /coarser levels in gsHTensorBasis - Multi-component DofMapper support for gsMultibasis::getMapper - Initialization of DoFmapper using BCS (taken from gsFESpace)

filiatra · 2025-10-25T12:01:22Z

I think that the multiple constructors are not needed, the should be only one with gsFunctionSet
This accepts all other objects

filiatra

I think that the multiple constructors are not needed, the should be only one with gsFunctionSet
This accepts all other objects.

Also it would be nice to avoid the new inclusion of gsBoxTopology (maybe just move the function body to cpp file.

stefantakacs · 2025-12-10T10:21:05Z

Do you think that the changes to the GaussSeidel preconditiner are necessary?

After template instanciation, the compiler only sees for example

void step(const gsMatrix<T> & rhs, gsMatrix<T> & x) const
    {
        if ( gsGaussSeidel::forward == gsGaussSeidel::forward )
            internal::gaussSeidelSweep<T>(m_expr,x,rhs);
        if ( gsGaussSeidel::forward == gsGaussSeidel::reverse )
            internal::reverseGaussSeidelSweep<T>(m_expr,x,rhs);
        if ( gsGaussSeidel::forward == gsGaussSeidel::symmetric )
        {
            internal::gaussSeidelSweep<T>(m_expr,x,rhs);
            internal::reverseGaussSeidelSweep<T>(m_expr,x,rhs);
        }
    }

which immediately simplifies to

void step(const gsMatrix<T> & rhs, gsMatrix<T> & x) const
    {
        internal::gaussSeidelSweep<T>(m_expr,x,rhs);
    }

I do not see the need for any enable_if magic. For newer compilers a constexpr-if would be feasible

Revert Gauss Seidel enable_if's Replace gsMappedBasis specialization in gsFeSpace

Copilot

Pull request overview

This PR enhances the sparse solver framework with custom preconditioners and significantly improves multi-grid support for hierarchical splines. The changes enable users to integrate Gismo preconditioners with Eigen's iterative solvers and provide comprehensive grid hierarchy construction methods for hierarchical tensor B-spline bases.

Key changes:

Added gsPreconditionerWrapper to bridge Gismo preconditioners with Eigen iterative solvers, enabling custom preconditioners in CG and BiCGSTAB
Implemented hierarchical coarsening methods for gsGridHierarchy that work with gsHTensorBasis, including new buildByHierarchicalCoarsening functionality
Extended gsHTensorBasis with level-based refinement/unrefinement methods (refineToLevel, unrefineToLevel, etc.) and changed transfer matrices to RowMajor format for multi-grid compatibility

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 26 comments.

Show a summary per file

File	Description
`src/gsSolver/gsPreconditioner.h`	Introduces `gsPreconditionerWrapper` class to adapt Gismo preconditioners for Eigen solvers
`src/gsMultiGrid/gsGridHierarchy.hpp`	Implements new grid hierarchy building methods with boundary conditions and hierarchical coarsening support
`src/gsMultiGrid/gsGridHierarchy.h`	Declares new overloads for grid hierarchy construction with component and BC parameters
`src/gsMatrix/gsSparseSolver.h`	Adds `CGCustom` and `BiCGSTABCustom` solver types and `solveWithGuess` interface for iterative solvers
`src/gsIO/gsXml*.cpp/hpp/h`	Extends XML serialization to support both `RowMajor` and `ColMajor` sparse matrices via template parameters
`src/gsHSplines/gsTHBSpline.hpp`	Updates transfer matrix type to `RowMajor` for consistency
`src/gsHSplines/gsHTensorBasis.hpp`	Implements level-based refinement/unrefinement methods and updates transfer matrix types to `RowMajor`
`src/gsHSplines/gsHTensorBasis.h`	Declares new refinement/unrefinement methods with transfer and coefficient update variants
`src/gsExpressions/gsFeSpace.h`	Refactors mapper initialization to use new `gsDofMapper` constructors, simplifying BC handling
`src/gsCore/gsMultiBasis.hpp`	Updates `combineTransferMatrices` to handle multiple components and adds assertions for validation
`src/gsCore/gsMultiBasis.h`	Extends `getMapper` methods with component count parameters and comprehensive documentation
`src/gsCore/gsLinearAlgebra.h`	Defines `CGCustom` and `BiCGSTABCustom` types in Eigen adaptor
`src/gsCore/gsForwardDeclarations.h`	Adds forward declaration for `gsPreconditionerWrapper`
`src/gsCore/gsDofMapper*.cpp/hpp/h`	Refactors with new constructors supporting topology, boundary conditions, and components; adds helper methods
`examples/sparseSolvers_example.cpp`	Demonstrates usage of custom preconditioner with CG solver
`examples/linearSolvers_example.cpp`	Adds example using custom Gismo preconditioner with Eigen CG solver

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src/gsCore/gsLinearAlgebra.h

src/gsHSplines/gsHTensorBasis.hpp

src/gsCore/gsDofMapper.hpp

Copilot · 2025-12-18T21:34:13Z

src/gsCore/gsDofMapper.h

+    GISMO_DEPRECATED
    template<class T>
    gsDofMapper(
-        const gsMultiBasis<T>         &bases,
+        const gsFunctionSet<T>         &bases,
        const gsBoundaryConditions<T> &dirichlet,
        int unk = 0
        ) : m_shift(0), m_bshift(0)
    {
-      init(bases, dirichlet, unk); //obsolete, one component
+        init(bases, dirichlet, unk); //obsolete, one component
+    }


The GISMO_DEPRECATED macro is applied to a constructor that takes gsFunctionSet instead of gsMultiBasis. However, the newer constructors below also take gsFunctionSet or gsMultiBasis. This deprecation seems inconsistent with the new API design where gsFunctionSet is the more general base class. The deprecation should either be removed or the reasoning should be clarified in a comment.

src/gsSolver/gsPreconditioner.h

src/gsCore/gsMultiBasis.hpp

src/gsCore/gsMultiBasis.h

src/gsCore/gsDofMapper.h

src/gsMatrix/gsSparseSolver.h

Co-authored-by: Copilot <[email protected]>

hverhelst added 7 commits September 5, 2025 15:26

ADD

6fc3f69

- Functions for refinement and coarsening of finer /coarser levels in gsHTensorBasis - Multi-component DofMapper support for gsMultibasis::getMapper - Initialization of DoFmapper using BCS (taken from gsFESpace)

add fwd decl

3b639d2

add gsDofMapper definitions

e2ce68c

add solveWithGuess

2f4d8bc

restrict levels in gridHierarchy

4eeafcb

fix DoFMapper compiler error in Pardiso

22d973d

add support for RowMajor sparse matrix XML export

c6e704a

hverhelst self-assigned this Oct 21, 2025

hverhelst requested a review from stefantakacs October 21, 2025 13:24

filiatra approved these changes Oct 25, 2025

View reviewed changes

filiatra requested changes Oct 25, 2025

View reviewed changes

Clean DoFmapper inits and constructors

2003d72

Revert Gauss Seidel enable_if's Replace gsMappedBasis specialization in gsFeSpace

hverhelst marked this pull request as ready for review December 18, 2025 21:20

Copilot AI review requested due to automatic review settings December 18, 2025 21:20

hverhelst requested a review from a team as a code owner December 18, 2025 21:20

hverhelst requested a review from filiatra December 18, 2025 21:20

Copilot started reviewing on behalf of hverhelst December 18, 2025 21:21 View session

hverhelst added the enhancement label Dec 18, 2025

Copilot AI reviewed Dec 18, 2025

View reviewed changes

hverhelst and others added 9 commits December 18, 2025 22:36

forgotten file

d025c2e

Update src/gsHSplines/gsHTensorBasis.hpp

099b38d

Co-authored-by: Copilot <[email protected]>

Update src/gsCore/gsDofMapper.hpp

ad109dc

Co-authored-by: Copilot <[email protected]>

Update src/gsSolver/gsPreconditioner.h

a01539f

Co-authored-by: Copilot <[email protected]>

Update src/gsCore/gsLinearAlgebra.h

d8cceb9

Co-authored-by: Copilot <[email protected]>

Update src/gsHSplines/gsHTensorBasis.hpp

f4bbaf0

Co-authored-by: Copilot <[email protected]>

Update src/gsHSplines/gsHTensorBasis.h

adc23ca

Co-authored-by: Copilot <[email protected]>

Update src/gsCore/gsDofMapper.h

7b27d7b

Co-authored-by: Copilot <[email protected]>

Update src/gsCore/gsMultiBasis.h

549e308

Co-authored-by: Copilot <[email protected]>

hverhelst and others added 6 commits December 18, 2025 22:54

Update src/gsCore/gsMultiBasis.hpp

90e97da

Co-authored-by: Copilot <[email protected]>

Merge branch 'multigrid' of github.com:gismo/gismo into multigrid

f482a57

small things, thanks @copilot

f94a75c

Update src/gsSolver/gsPreconditioner.h

a5c6e51

Co-authored-by: Copilot <[email protected]>

Merge remote-tracking branch 'origin/multigrid' into multigrid

fb31601

Fix failing tests

15b38e2

Provide feedback

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Enrichment of sparse-solvers, improved Multi-grid support (incl. hierarchical splines) #839

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hverhelst commented Oct 21, 2025 •

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Enrichment of sparse-solvers, improved Multi-grid support (incl. hierarchical splines) #839

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hverhelst commented Oct 21, 2025 •

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