Enable coupled dof equation condition in 3d by m-frey · Pull Request #1751 · 4C-multiphysics/4C

m-frey · 2026-02-11T16:05:46Z

Description and Context

This PR enables PointLinearCoupledEquation constraints for 3D displacement coupling by adding support for the dispz degree of freedom. There are no additional test as the underlying functionality is already tested in 3d.

Copilot

Pull request overview

Enables PointLinearCoupledEquation constraints for 3D displacement coupling by introducing support for the dispz degree of freedom in both input validation and MPC assembly.

Changes:

Allow ADD: "dispz" in the DESIGN POINT COUPLED DOF EQUATION CONDITIONS input schema.
Map dispz to the third displacement DOF index when building linear MPC equations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
`src/constraint_framework/4C_constraint_framework_submodelevaluator_mpc.cpp`	Adds `dispz` DOF mapping for linear coupled equation MPC construction.
`src/constraint_framework/4C_constraint_framework_input.cpp`	Extends the allowed `ADD` selection list to include `dispz`.

Comments suppressed due to low confidence (1)

src/constraint_framework/4C_constraint_framework_submodelevaluator_mpc.cpp:643

The exception message still says linear coupled equations are only implemented for 2D (dispx/dispy), but dispz is now accepted above. Update the error text to reflect the actual supported DOFs and (ideally) mention that dispz requires a 3D problem/RVE.

      FOUR_C_THROW(
          "Linear coupled equations (MPCs) are only implemented for 2D (dispx or dispy DOFs)");
    }

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Copilot · 2026-02-11T16:19:38Z

src/constraint_framework/4C_constraint_framework_submodelevaluator_mpc.cpp

+    else if (dofStr == "dispz")
+    {
+      dofPos = 2;
+    }


dispz is now mapped to dofPos = 2, but there is no guard that the current problem/RVE actually has a third displacement DOF. In a 2D setup, this will likely index discret_ptr_->dof(node)[2] out of range. Add a dimension/DOF-count check (e.g., based on rve_dim_ or discret_ptr_->dof(node).size()) and throw a clear error when dispz is used in 2D.

Copilot · 2026-02-11T16:19:38Z

src/constraint_framework/4C_constraint_framework_input.cpp

      Core::Conditions::PointLinearCoupledEquation, false, Core::Conditions::geometry_type_point);

  linear_ce.add_component(parameter<int>("EQUATION", {.description = "EQUATION"}));
-  linear_ce.add_component(deprecated_selection<std::string>("ADD", {"dispx", "dispy", "undefined"},
-      {.description = "degrees of freedom", .default_value = "undefined"}));
+  linear_ce.add_component(
+      deprecated_selection<std::string>("ADD", {"dispx", "dispy", "dispz", "undefined"},


The condition definition text right above still describes the coupled DOF equation as being for "2d", but the allowed DOFs now include dispz (3D). Please update the human-readable description so the input schema matches the actual capabilities and doesn't mislead users.

Copilot · 2026-02-11T16:19:39Z

src/constraint_framework/4C_constraint_framework_input.cpp

+  linear_ce.add_component(
+      deprecated_selection<std::string>("ADD", {"dispx", "dispy", "dispz", "undefined"},
+          {.description = "degrees of freedom", .default_value = "undefined"}));


Adding dispz changes supported input behavior, but there is no regression test covering a 3D DESIGN POINT COUPLED DOF EQUATION CONDITIONS term with ADD: "dispz". Consider adding a 3D integration test input (similar to tests/input_files/rve3d_periodic_bcs.4C.yaml, but including a PointLinearCoupledEquation section with dispz) and registering it in tests/list_of_tests.cmake (there is already a 2D MPC test: rve2d_periodic_bcs_with_mpcs.4C.yaml).

isteinbrecher

Looks good to me, can you add a small test case for this feature?

maxfirmbach

@m-frey I just have a small remark. I would also like to see a test that explicitly uses the new feature e.g. ADD: "dispz" somewhere.

maxfirmbach · 2026-02-24T07:41:04Z

src/constraint_framework/4C_constraint_framework_submodelevaluator_mpc.cpp

    else
    {
      FOUR_C_THROW(
          "Linear coupled equations (MPCs) are only implemented for 2D (dispx or dispy DOFs)");


I think this error message also has to be adapted right?

ischeider

Just asking for some more documentation ;-)

ischeider · 2026-03-04T10:28:50Z

src/constraint_framework/4C_constraint_framework_input.cpp

@@ -110,8 +110,9 @@
      Core::Conditions::PointLinearCoupledEquation, false, Core::Conditions::geometry_type_point);

  linear_ce.add_component(parameter<int>("EQUATION", {.description = "EQUATION"}));


Could you please also change the description of EQUATION to something more useful? What kind of equation is possible, with which dependencies? See also comment to COEFFICIENT.
If it refers to a function, then shouldn't we redefine the parameter to FUNCT, which is the name that we use in general? Even though it is a breaking change then.

ischeider · 2026-03-04T10:30:02Z

src/constraint_framework/4C_constraint_framework_input.cpp

+  linear_ce.add_component(
+      deprecated_selection<std::string>("ADD", {"dispx", "dispy", "dispz", "undefined"},
+          {.description = "degrees of freedom", .default_value = "undefined"}));
  linear_ce.add_component(parameter<double>("COEFFICIENT"));


The coefficient does not have a description at all. Since there is also EQUATION available, I don't know what an additional coefficient could do (maybe I fully misunderstand the parameters). If it is a factor added to the function/equation, I recommend to make it optional with 1 as a default value.

ischeider · 2026-03-04T10:45:29Z

src/constraint_framework/4C_constraint_framework_input.cpp

  /*----------------------------------------------------------------------*/
  Core::Conditions::ConditionDefinition linear_ce("DESIGN POINT COUPLED DOF EQUATION CONDITIONS",
      "PointLinearCoupledEquation",
      "definition of the term of a linear couple equation coupling different degrees of "


Suggested change

"Definition of the term of a linear couple equation coupling specified degrees of "

isteinbrecher

Can we add a test case for this feature?

Enable coupled dof equation condition in 3d

3b0f8c3

m-frey self-assigned this Feb 11, 2026

m-frey requested review from Copilot, isteinbrecher and maxfirmbach February 11, 2026 16:05

Copilot started reviewing on behalf of m-frey February 11, 2026 16:16 View session

Copilot AI reviewed Feb 11, 2026

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isteinbrecher reviewed Feb 11, 2026

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m-frey mentioned this pull request Feb 21, 2026

Remove untested penalty-based 3D multipoint constraint #1774

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maxfirmbach requested changes Feb 24, 2026

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ischeider reviewed Mar 4, 2026

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Enable coupled dof equation condition in 3d#1751

Enable coupled dof equation condition in 3d#1751
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m-frey:Enable-coupled-dof-equation-condition-in-3d

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		@@ -110,8 +110,9 @@
		Core::Conditions::PointLinearCoupledEquation, false, Core::Conditions::geometry_type_point);

		linear_ce.add_component(parameter<int>("EQUATION", {.description = "EQUATION"}));


	"Definition of the term of a linear couple equation coupling specified degrees of "

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m-frey commented Feb 11, 2026

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