# \#linear-algebra

**URL:** https://fenicsproject.discourse.group/tag/linear-algebra/41.md

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## [Scaling of condition number in 1D, 2D, and 3D](https://fenicsproject.discourse.group/t/scaling-of-condition-number-in-1d-2d-and-3d/18462)

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**Author:** [@Haydel\_Collins](https://fenicsproject.discourse.group/u/Haydel_Collins)\
**Replies:** 6\
**Last updated:** [December 15, 2025, 8:56pm UTC](https://fenicsproject.discourse.group/t/scaling-of-condition-number-in-1d-2d-and-3d/18462 "2025-12-15T20:56:26Z")

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My understanding is that the condition number (for stiffness matrix of poisson) should scale like h^-2. Here is a MWE, more or less from the demos, where I run this for a few levels of refinement using nx = \[10,20,40,80…

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## [Precondition appears not to happen](https://fenicsproject.discourse.group/t/precondition-appears-not-to-happen/15969)

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**Author:** [@Stein](https://fenicsproject.discourse.group/u/Stein)\
**Replies:** 4\
**Last updated:** [November 13, 2024, 10:40am UTC](https://fenicsproject.discourse.group/t/precondition-appears-not-to-happen/15969 "2024-11-13T10:40:21Z")

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Hi all, For a Navier-Stokes problem, I want to separately precondition the u block (Jacobi) and the p block (algebraic multigrid on the Schur complement), while using mixed spaces. I believe I have everything set up co…

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## [ReferenceGrad error with Quad elements](https://fenicsproject.discourse.group/t/referencegrad-error-with-quad-elements/16061)

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**Author:** [@r4ge199](https://fenicsproject.discourse.group/u/r4ge199)\
**Replies:** 0\
**Last updated:** [October 18, 2024, 5:41am UTC](https://fenicsproject.discourse.group/t/referencegrad-error-with-quad-elements/16061 "2024-10-18T05:41:14Z")

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I am trying to implement a structural shell analysis formulation. It works with triangular elements but whenever I switch to quads, the code throws an error “Currently no support for ReferenceGrad in CoefficientDerivativ…

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## [Evaluation of grad(u) at a point x\_ref for variational formulation](https://fenicsproject.discourse.group/t/evaluation-of-grad-u-at-a-point-x-ref-for-variational-formulation/16020)

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**Author:** [@Hell](https://fenicsproject.discourse.group/u/Hell)\
**Replies:** 2\
**Last updated:** [October 11, 2024, 6:46am UTC](https://fenicsproject.discourse.group/t/evaluation-of-grad-u-at-a-point-x-ref-for-variational-formulation/16020 "2024-10-11T06:46:32Z")

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Hello everyone, I am trying to solve the following problem in its variational form: In the first step, I want to solve the homogeneous eigenvalue problem, where the right-hand side is set to 0. I am using SLEPc for …

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## [Question about dolfin.cpp.la.Matrix](https://fenicsproject.discourse.group/t/question-about-dolfin-cpp-la-matrix/13687)

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**Author:** [@xiaohe](https://fenicsproject.discourse.group/u/xiaohe)\
**Replies:** 8\
**Last updated:** [February 24, 2024, 12:03pm UTC](https://fenicsproject.discourse.group/t/question-about-dolfin-cpp-la-matrix/13687 "2024-02-24T12:03:02Z")

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Hello, everyone I am working on fenics 2019.1, I have some question about the class dolfin.cpp.la.Matrix Whether fenics supports basic matrix operations.(for example add,subract, multiply, divide, inv…) Whether fenics…