[Core][Future] Including linear operators to future environment #14119

rubenzorrilla · 2026-01-09T16:29:01Z

📝 Description
In this PR I'm introducing the LinearOperator classes in #14110 to the future environment, namely strategies, schemes, builders and linear solvers.

Note that I also took the chance to rename the LinearSystemContainer to ImplicitStrategyDataContainer, something that is much more self-descriptive IMO.

This requires #14108 and #14110 to be merged first but I'd like to create it as a draft PR to start the discussion and triggering the CI.

loumalouomega · 2026-01-09T16:38:21Z

kratos/future/linear_operators/linear_operator.h

+///@{
+
+/**
+ * @brief


Repeated and empty

Suggested change

* @brief

loumalouomega · 2026-01-09T16:38:48Z

kratos/future/linear_operators/linear_operator.h

+    TMatrixType& GetMatrix()
+    {
+        KRATOS_ERROR_IF(this->IsMatrixFree()) << "Trying to access matrix from a matrix-free LinearOperator." << std::endl;
+        auto r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as std::any


&?

Suggested change

auto r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as std::any

auto& r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as std::any

Okay, you do a cast later, remove the r?

loumalouomega · 2026-01-09T16:39:51Z

kratos/future/linear_operators/linear_operator.h

+    const TMatrixType& GetMatrix() const
+    {
+        KRATOS_ERROR_IF(this->IsMatrixFree()) << "Trying to access matrix from a matrix-free LinearOperator." << std::endl;
+        const auto r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as const std::any


loumalouomega · 2026-01-09T16:40:24Z

kratos/future/linear_solvers/amgcl_solver.h

 * AMGCL is a header-only C++ library for solving large sparse linear systems with algebraic multigrid (AMG) method. AMG is one of the most effective iterative methods for solution of equation systems arising, for example, from discretizing PDEs on unstructured grids. The method can be used as a black-box solver for various computational problems, since it does not require any information about the underlying geometry. AMG is often used not as a standalone solver but as a preconditioner within an iterative solver (e.g. Conjugate Gradients, BiCGStab, or GMRES).
 * AMGCL builds the AMG hierarchy on a CPU and then transfers it to one of the provided backends. This allows for transparent acceleration of the solution phase with help of OpenCL, CUDA, or OpenMP technologies. Users may provide their own backends which enables tight integration between AMGCL and the user code.
- * @author Denis Demidov
+ * @author Pooyan Dadvand


loumalouomega · 2026-01-09T16:41:17Z

kratos/future/linear_solvers/iterative_solver.h

@@ -23,6 +22,7 @@
 // Project includes
 #include "includes/define.h"


This can be safely removed

Suggested change

#include "includes/define.h"

Any case now with C++20 we can use the modules to reduce compilations times and avoid the infinite nested includes

loumalouomega · 2026-01-09T16:43:54Z

kratos/future/linear_solvers/preconditioner.h

@@ -22,6 +22,7 @@
 // Project includes
 #include "includes/define.h"


Suggested change

#include "includes/define.h"

loumalouomega · 2026-01-09T16:44:30Z

kratos/future/linear_solvers/preconditioner.h

@@ -22,6 +22,7 @@
 // Project includes
 #include "includes/define.h"
 #include "includes/model_part.h"


Suggested change

#include "includes/model_part.h"

Linear operator already includes it

loumalouomega · 2026-01-09T16:44:48Z

kratos/future/linear_solvers/skyline_lu_factorization_solver.h


 // Project includes
-#include "future/linear_solvers/direct_solver.h"
 #include "includes/define.h"


Suggested change

#include "includes/define.h"

loumalouomega · 2026-01-09T16:45:33Z

kratos/future/solving_strategies/builders/builder.h

-#include "containers/csr_matrix.h"
-#include "containers/system_vector.h"
-#include "containers/sparse_contiguous_row_graph.h"
 #include "includes/define.h"


Suggested change

#include "includes/define.h"

loumalouomega · 2026-01-09T16:45:50Z

kratos/future/solving_strategies/builders/elimination_builder.h

-#include "containers/csr_matrix.h"
-#include "containers/system_vector.h"
-#include "containers/sparse_contiguous_row_graph.h"
 #include "includes/define.h"


Suggested change

#include "includes/define.h"

loumalouomega · 2026-01-09T16:46:34Z

kratos/future/solving_strategies/schemes/static_scheme.h

 {
 public:

    // FIXME: Does not work... ask @Charlie


loumalouomega

Some comments

philbucher · 2026-01-26T17:20:15Z

This looks cool. In fact I was also looking into this lately. Matrix free only works with iterative solvers right? Does amgcl support it?

RiccardoRossi · 2026-01-27T09:29:38Z

This looks cool. In fact I was also looking into this lately. Matrix free only works with iterative solvers right? Does amgcl support it?

yes, it only works with krylov solvers. The problem is that typically it is impossible to mount a preconditioner. No ... AMGCL does not support it...

cool thing is that you can also use to mount a GMRES-krylov solver for nonlinear problem

philbucher · 2026-01-27T09:45:23Z

yes, it only works with krylov solvers.

is it worth it then? Seems that you are doing substantial changes to accommodate it. (I have no idea, just curious)

RiccardoRossi · 2026-01-27T11:40:51Z

Linear Operators are a nice thing to have, but they are not the reason of being of the reorganization we are doing.

rather we are revamping the strategy/solver design to be more modular and to better consider parallelism (for exampel mpi will now be native) and the application of constraints

rubenzorrilla added 30 commits November 6, 2025 17:08

First LinearOperator class implementation

64e20e8

Merge branch 'master' into core/future-linear-operator

7396076

Merge branch 'master' into core/future-linear-operator

b288bea

Merge branch 'master' into core/future-linear-operator

78a5360

Advances (not working)

4dbd1db

Working version

5c9c6bf

Merge branch 'master' into core/future-linear-operator

1cdecbf

FCT process c++20 fix

b7be08d

Preliminary working version

55b6363

Advances in the new design (not working yet)

bd1871b

More advances (still not working)

c32a0b6

Fix warning in distributed CSR matrix

ee8868d

Compiling (strategies not working yet)

0a9376c

Merge branch 'master' into core/future-linear-operator

06dbc96

Minor fix in strategies (WORKING NEW VERSION)

b4ac3f5

Merge branch 'master' into core/future-linear-operator

23e1cbe

Using std::any

17873b4

Nice & Clean (working version w/ std::any and linalg defines)

9dfc701

Minors

aed78d5

Better name for linear system container

7d22909

Remove linear operator variadic alternative

712fdb2

Fix autorship

77c216f

Fix autorship

de88ab8

Revert Python export

8e51e8a

Add linear algebra defines

39d5e0f

Revert no longer needed changes in distributed CSR

a020766

Rename linear operator test file

3845634

Delete file

075bc14

Test

94fc666

Matrix-free and CSR linear operators

e4f1d55

rubenzorrilla added Feature Usability labels Jan 9, 2026

loumalouomega reviewed Jan 9, 2026

View reviewed changes

kratos/future/linear_operators/linear_operator.h

///@{

/**

* @brief

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Repeated and empty

Suggested change

* @brief

loumalouomega reviewed Jan 9, 2026

View reviewed changes

kratos/future/solving_strategies/schemes/static_scheme.h

{

public:

// FIXME: Does not work... ask @Charlie

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@roigcarlo

loumalouomega reviewed Jan 9, 2026

View reviewed changes

rubenzorrilla added 10 commits January 9, 2026 17:56

Minor fixes

f8a807d

Merge branch 'master' into core/future-linear-operator

dfd0281

Preliminary implementation.

8ce7781

Advances in the design

58559ca

Working

7f823fd

Compiling advances (strategies tests not working yet)

f315442

WORKING VERSION W/ LINEAR SYSTEM

5faa4b2

Minor

45a05cb

Move implicit strategy container

c76d81b

Container clean up

0acb62a

Minor

4d883f8

rubenzorrilla mentioned this pull request Jan 27, 2026

[Core][Future] Add linear system container #14161

Open

	auto r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as std::any
	auto& r_matrix = this->GetMatrixImpl(); // Get the underlying matrix as std::any

		@@ -23,6 +22,7 @@
		// Project includes
		#include "includes/define.h"

		@@ -22,6 +22,7 @@
		// Project includes
		#include "includes/define.h"

[Core][Future] Including linear operators to future environment #14119

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[Core][Future] Including linear operators to future environment #14119

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philbucher commented Jan 26, 2026

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RiccardoRossi commented Jan 27, 2026

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