[petsc-users] Additiional DoF per cell
Matthew Knepley
knepley at gmail.com
Fri May 8 15:28:58 CDT 2026
On Fri, May 8, 2026 at 3:34 PM Noam T. <dontbugthedevs at proton.me> wrote:
> I was indeed confused before regarding how the element ended up with 3
> unknowns.
>
> So for a P1, having three unknowns, means the field is interpolated as p =
> po + p1*x + p2*y?
> Then P2 has 6 components (total dim = 14), which agrees with a complete
> 2nd order polynomial.
>
> Then my question is, how can I have any other number of components? In
> particular, some of the implementations I am looking at use 4 and 7
> additional DoF. Will this require a new field per DoF?
>
No, you start with how these fields are supposed to behave. If you say
I have a field that gives me five constant values in every cell
Then you have a P0 field with five components, which will add 5 dofs to the
DS. If instead you say
I have a field that gives two values linearly interpolated over each cell
Then you have a P1 field with two components, which will add 6 dofs (with
triangles) to the DS.
Thanks,
Matt
> Thanks,
> Noam
> On Friday, May 8th, 2026 at 7:13 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
> On Fri, May 8, 2026 at 2:54 PM Noam T. <dontbugthedevs at proton.me> wrote:
>
>> Code attached.
>>
>
> I think you misunderstand the definition of the element. I do not think
> you want 3 components for your pressure. You want 1 component. It is a
> scalar variable. In my original example, I had a single component.
> Components create tensor spaces.
>
> If you are using discontinuous P1, then it has 3 unknowns, which is what I
> think you are trying to specify. You should change the space you are using
> if you want to change the number of variables.
>
> Does that clear it up?
>
> Thanks,
>
> Matt
>
>> Noticed from PetscSectionView:
>>
>> PetscSectionSym Object: 1 MPI process
>> type: label
>> Label 'depth'
>> Symmetry for stratum value 0 (0 dofs per point): no symmetries
>> Symmetry for stratum value 1 (0 dofs per point): no symmetries
>> Symmetry for stratum value 2 (12 dofs per point): <----------------------
>> 12 DoF ?
>> Orientation range: [-4, 4)
>> Symmetry for stratum value -1 (0 dofs per point): no symmetries
>>
>> Thanks,
>> Noam
>>
>> On Friday, May 8th, 2026 at 3:58 PM, Noam T. <dontbugthedevs at proton.me>
>> wrote:
>>
>> This is likely to be a Section construction problem again. The Section
>> fields are separated by DMPlexVecGetClosure(), sp you must not have defined
>> the fields in the Section. If you put these calls into the code that I sent
>> you, what do you get?
>>
>>
>> If I use the exact same arrays/values for constructing the section, I get
>> the same closure arrangement in the code you provided. Not surprising I
>> guess? A seemingly random number of coordinates / zeroes / more coordinates.
>>
>> I checked example 14 (
>> https://urldefense.us/v3/__https://petsc.org/release/src/dm/impls/plex/tutorials/ex14.c.html__;!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMnouheZB$ ) for
>> constructing the section. These are the values I used:
>>
>> - n_fields = 2
>>
>> - numDof [n_fields*(dim+1)] = numDof[2*(2+1)] = [2 0 0 0 0 N]
>>
>> The u field is defined in the nodes, with 2 components (u, v), hence the
>> first "2". Then no components for edges/faces.
>> For the p field, what I am trying to simulate is having nc (independent)
>> DoF, sort of like having nc scalar fields, if that makes sense? Hence using:
>>
>> - N = nc
>> - Also using the flag "-pres_petscspace_degree 0"
>>
>> But I'm not sure about those values.
>>
>> Then for simplicity numBC = 0 and all other arguments are NULL (will deal
>> with boundary conditions later).
>>
>> With these arguments, I get the same as before e.g.
>>
>> -- nc = 3 (total dimension = 11)
>> closure = y1 x2 y2 x3 y3 0 0 0 x0 y0 x1
>>
>> Thanks,
>> Noam
>>
>> On Friday, May 8th, 2026 at 1:25 PM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>> On Fri, May 8, 2026 at 8:01 AM Noam T. <dontbugthedevs at proton.me> wrote:
>>
>>> Moving on to the values of the closure.
>>>
>>> Initially I create a vector for the DM with DMCreateLocal/GlobalVector,
>>> which is used for e.g. the solution. Following the example before, it will
>>> have size 8 (coordinates) + nc (for the p field).
>>>
>>> I am getting a seemingly random order when I test with different values
>>> of nc. Say, I initialize the vector (VecSetValues) with the coordinates
>>> x_i, y_i . The rest nc components are set to zero. The closure returns:
>>>
>>> -- nc = 1
>>> closure = y0 x1 y1 x2 y2 x3 y3 0 x0
>>>
>>> -- nc = 3
>>> closure = y1 x2 y2 x3 y3 0 0 0 x0 y0 x1
>>>
>>> -- nc = 7
>>> closure = y3 0 0 0 0 0 0 0 x0 y0 x1 y1 x2 y2
>>>
>>> Looking at that output:
>>> - The first value is always a y coordinate (second component of u field).
>>> - The position of the nc = 0 components change (starting with nc = 8,
>>> all zero values come first, followed by the coordinates).
>>>
>>> Looking again at ex77.c (
>>> https://urldefense.us/v3/__https://petsc.org/release/src/snes/tutorials/ex77.c.html__;!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMov1NT81$ ), it says the
>>> closure stacks up the fields, which aligns with the output above (all u
>>> values, then all p values), but which is the starting point seems arbitrary.
>>>
>>
>> This is likely to be a Section construction problem again. The Section
>> fields are separated by DMPlexVecGetClosure(), sp you must not have defined
>> the fields in the Section. If you put these calls into the code that I sent
>> you, what do you get?
>>
>> Thanks,
>>
>> Matt
>>
>>> The vector is initialized as [x0 y0 .... x3 y3 0 0 ... 0], which may not
>>> be correct to start with.
>>>
>>> I noticed I could instead use DMPlexVecGetClosureAtDepth( ..., depth =
>>> 0, ...) so that I only get the u field DoF. But I will need to deal with
>>> the p field values as well at some point.
>>>
>>> Thanks,
>>> Noam
>>>
>>> On Friday, May 8th, 2026 at 11:05 AM, Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>> On Fri, May 8, 2026 at 5:08 AM Noam T. <dontbugthedevs at proton.me> wrote:
>>>
>>>> On the plus side, using the flags you provided in the previous email
>>>>
>>>> -dm_plex_simplex 0 -mech_petscspace_degree 1 -pres_petscspace_degree 1
>>>> -pres_petscspace_poly_tensor 0 -pres_petscdualspace_lagrange_continuity 0
>>>>
>>>> the output of -ds_view is identical to yours, so setting up the fields
>>>> should be correct.
>>>> Thanks. I forgot about the flag "-[]_petscdualspace_lagrange_continuity
>>>> 0" so as to have a discontinuous field.
>>>>
>>>> However, the closure size was still wrong.
>>>>
>>>> But, I figured out the reason: the manual set up of the section.
>>>> For the argument "numDof" in DMPlexCreateSection(), I was computing the
>>>> number of DoF with PetscSectionGetDof() (which was fine until now, since
>>>> there was a single field), instead of PetscSectionGetFieldDof().
>>>> So as you previously suggested
>>>>
>>>> [...] It sounds like somehow you have a copy of your fields.
>>>>
>>>>
>>>> the number of DoF per field were indeed "doubled" with the sum of both
>>>> fields.
>>>>
>>>
>>> Excellent. Let me know if you have any more issues.
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>>> Thanks,
>>>> Noam
>>>>
>>>> On Wednesday, May 6th, 2026 at 2:06 PM, Matthew Knepley <
>>>> knepley at gmail.com> wrote:
>>>>
>>>> Okay, this is a problem with specifying the space I believe. You want a
>>>> discontinuous space for pressure.
>>>>
>>>> Here is what I get
>>>>
>>>> Discrete System with 2 fields
>>>> cell total dim 11 total comp 3
>>>> Field Q1 FEM 2 components (implicit) (Nq 4 Nqc 1) 1-jet
>>>> PetscFE Object: Q1 (mech_) 1 MPI process
>>>> type: vector
>>>> Vector Finite Element in 2 dimensions with 2 components
>>>> PetscSpace Object: Q1 (mech_) 1 MPI process
>>>> type: sum
>>>> Space in 2 variables with 2 components, size 8
>>>> Sum space of 2 concatenated subspaces (all identical)
>>>> PetscSpace Object: Q1 (mech_sumcomp_) 1 MPI process
>>>> type: tensor
>>>> Space in 2 variables with 1 components, size 4
>>>> Tensor space of 2 subspaces (all identical)
>>>> PetscSpace Object: sum component tensor component
>>>> (mech_sumcomp_tensorcomp_) 1 MPI process
>>>> type: poly
>>>> Space in 1 variables with 1 components, size 2
>>>> Polynomial space of degree 1
>>>> PetscDualSpace Object: Q1 (mech_) 1 MPI process
>>>> type: sum
>>>> Dual space with 2 components, size 8
>>>> Sum dual space of 2 concatenated subspaces (all identical)
>>>> PetscDualSpace Object: Q1 1 MPI process
>>>> type: lagrange
>>>> Dual space with 1 components, size 4
>>>> Continuous tensor Lagrange dual space
>>>> Quadrature on a quadrilateral of order 3 on 4 points (dim 2)
>>>> Field Q1 FEM 1 component (implicit) (Nq 4 Nqc 1) 1-jet
>>>> PetscFE Object: Q1 (pres_) 1 MPI process
>>>> type: basic
>>>> Basic Finite Element in 2 dimensions with 1 components
>>>> PetscSpace Object: Q1 (pres_) 1 MPI process
>>>> type: poly
>>>> Space in 2 variables with 1 components, size 3
>>>> Polynomial space of degree 1
>>>> PetscDualSpace Object: Q1 (pres_) 1 MPI process
>>>> type: lagrange
>>>> Dual space with 1 components, size 3
>>>> Discontinuous Lagrange dual space
>>>> Quadrature on a quadrilateral of order 3 on 4 points (dim 2)
>>>> Weak Form System with 2 fields
>>>>
>>>> I have attached the code I used.
>>>>
>>>> Thanks,
>>>>
>>>> Matt
>>>>
>>>> On Wed, May 6, 2026 at 9:32 AM Noam T. <dontbugthedevs at proton.me>
>>>> wrote:
>>>>
>>>>>
>>>>> Field p FEM 3 components (implicit) (Nq 4 Nqc 1) 1-jet
>>>>>
>>>>>
>>>>> 1. Why does pressure have 3 components in 2D?
>>>>>
>>>>>
>>>>> I used nc = 3 when calling PetscFECreateDefault() for the pressure
>>>>> field. Confusion between wanting 3 addditional DoF and components.
>>>>>
>>>>> With nc = 1 the closure size is 18 instead.
>>>>>
>>>>> 2. Did you look at the incompressible example SNES ex69? It sets up
>>>>> this exact element.
>>>>>
>>>>>
>>>>> I changed some of my code following the example and got rid of some
>>>>> errors. But I'll have a more thorough look again.
>>>>>
>>>>> 3. Please send me that code that sets up your DM. It sounds like
>>>>> somehow you have a copy of your fields.
>>>>>
>>>>> Thanks,
>>>>>
>>>>>
>>>>> For reference, -ds_view with only one (displacements) fields shows:
>>>>>
>>>>> ---
>>>>> Discrete System with 1 fields
>>>>> cell total dim 8 total comp 2
>>>>> Field u FEM 2 components (implicit) (Nq 4 Nqc 1) 1-jet
>>>>> PetscFE Object: u (disp_) 1 MPI process
>>>>> type: vector
>>>>> Vector Finite Element in 2 dimensions with 2 components
>>>>> PetscSpace Object: Q1 (disp_) 1 MPI process
>>>>> type: sum
>>>>> Space in 2 variables with 2 components, size 8
>>>>> Sum space of 2 concatenated subspaces (all identical)
>>>>> PetscSpace Object: Q1 (disp_sumcomp_) 1 MPI process
>>>>> type: tensor
>>>>> Space in 2 variables with 1 components, size 4
>>>>> Tensor space of 2 subspaces (all identical)
>>>>> PetscSpace Object: sum component tensor component
>>>>> (disp_sumcomp_tensorcomp_) 1 MPI process
>>>>> type: poly
>>>>> Space in 1 variables with 1 components, size 2
>>>>> Polynomial space of degree 1
>>>>> PetscDualSpace Object: Q1 (disp_) 1 MPI process
>>>>> type: sum
>>>>> Dual space with 2 components, size 8
>>>>> Sum dual space of 2 concatenated subspaces (all identical)
>>>>> PetscDualSpace Object: Q1 1 MPI process
>>>>> type: lagrange
>>>>> Dual space with 1 components, size 4
>>>>> Continuous tensor Lagrange dual space
>>>>> Quadrature on a quadrilateral of order 3 on 4 points (dim 2)
>>>>> Weak Form System with 1 fields
>>>>> ---
>>>>>
>>>>> and -dm_view
>>>>>
>>>>> ---
>>>>> DM Object: 1 MPI process
>>>>> type: plex
>>>>> DM_0x55c117db1b00_2 in 2 dimensions:
>>>>> Number of 0-cells per rank: 4
>>>>> Number of 1-cells per rank: 4
>>>>> Number of 2-cells per rank: 1
>>>>> Labels:
>>>>> celltype: 3 strata with value/size (0 (4), 1 (4), 4 (1))
>>>>> depth: 3 strata with value/size (0 (4), 1 (4), 2 (1))
>>>>> Cell Sets: 1 strata with value/size (1 (1))
>>>>> surf: 1 strata with value/size (1 (1))
>>>>> Face Sets: 2 strata with value/size (2 (1), 3 (1))
>>>>> edge_right: 1 strata with value/size (3 (1))
>>>>> edge_left: 1 strata with value/size (2 (1))
>>>>> Vertex Sets: 4 strata with value/size (4 (1), 5 (1), 6 (1), 7 (1))
>>>>> P1: 1 strata with value/size (4 (1))
>>>>> P2: 1 strata with value/size (5 (1))
>>>>> P3: 1 strata with value/size (6 (1))
>>>>> P4: 1 strata with value/size (7 (1))
>>>>> Field u:
>>>>> adjacency FEM
>>>>> /// With the second field, the two lines below are added
>>>>> Field p:
>>>>> adjacency FEM
>>>>> ---
>>>>>
>>>>> DM set up
>>>>>
>>>>> DM :: dm_mesh
>>>>> PetscFE :: u_FE, p_FE
>>>>> PetscInt :: dim, dim_u_FE, tdim
>>>>> PetscDS :: dm_ds
>>>>>
>>>>>
>>>>> DMCreate(PETSC_COMM_WORLD, dm_mesh)
>>>>> DMSetType(dm_mesh, DMPLEX)
>>>>> DMGetDimension(dm_mesh, dim) // dim = 2
>>>>> DMSetFromOptions(dm_mesh) // this was called twice by mistake, now
>>>>> removed; no changes that I can see
>>>>>
>>>>> -- using flags
>>>>>
>>>>> -dm_plex_filename QUAD1.msh
>>>>> -dm_plex_interpolate 1
>>>>> -dm_plex_gmsh_use_generic
>>>>> -dm_plex_gmsh_use_regions
>>>>> -dm_plex_gmsh_multiple_tags
>>>>> -dm_plex_gmsh_mark_vertices
>>>>>
>>>>> -- some operations with labels
>>>>>
>>>>> // u field
>>>>> PetscFECreateDefault(PETSC_COMM_SELF, dim, dim, PETSC_FALSE, "mech_",
>>>>> PETSC_DETERMINE, u_FE)
>>>>> PetscFEGetDimension(u_FE, dim_u_FE) // dim_u_FE = 8
>>>>> DMAddField(dm_mesh, NULL, (PetscObject)u_FE)
>>>>>
>>>>> // p field
>>>>> PetscFECreateDefault(PETSC_COMM_SELF, dim , 1, PETSC_FALSE, "pres_",
>>>>> PETSC_DETERMINE, p_FE)
>>>>> PetscFEGetDimension(p_FE, dim_p_FE) // dim_p_FE = 1
>>>>> DMAddField(dm_mesh, NULL, (PetscObject)p_FE)
>>>>>
>>>>> DMCreateDS(dm_mesh)
>>>>> DMGetDS(dm_mesh, dm_DS)
>>>>> PetscDSGetTotalDimension(dm_DS, tdim) // tdim
>>>>>
>>>>> with flags
>>>>>
>>>>> -disp_petscdualspace_lagrange_node_type equispaced
>>>>> -disp_petscdualspace_lagrange_node_endpoints 1
>>>>>
>>>>>
>>>>> I believe these are all the DM related calls.
>>>>>
>>>>> Thanks,
>>>>> Noam
>>>>>
>>>>> On Wednesday, May 6th, 2026 at 11:39 AM, Matthew Knepley <
>>>>> knepley at gmail.com> wrote:
>>>>>
>>>>> On Wed, May 6, 2026 at 6:56 AM Noam T. <dontbugthedevs at proton.me>
>>>>> wrote:
>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> That is wrong. Are you sure about 22?
>>>>>>
>>>>>>
>>>>>> That's what I get, from the argument "csize" in
>>>>>> DMPlexGetVecClosure().
>>>>>>
>>>>>> Here's the output of PetscDSView:
>>>>>>
>>>>>> Discrete System with 2 fields
>>>>>> cell total dim 11 total comp 5
>>>>>> Field u FEM 2 components (implicit) (Nq 4 Nqc 1) 1-jet
>>>>>> PetscFE Object: u (mech_) 1 MPI process
>>>>>> type: vector
>>>>>> Vector Finite Element in 2 dimensions with 2 components
>>>>>> PetscSpace Object: Q1 (mech_) 1 MPI process
>>>>>> type: sum
>>>>>> Space in 2 variables with 2 components, size 8
>>>>>> Sum space of 2 concatenated subspaces (all identical)
>>>>>> PetscSpace Object: Q1 (mech_sumcomp_) 1 MPI process
>>>>>> type: tensor
>>>>>> Space in 2 variables with 1 components, size 4
>>>>>> Tensor space of 2 subspaces (all identical)
>>>>>> PetscSpace Object: sum component tensor component
>>>>>> (mech_sumcomp_tensorcomp_) 1 MPI process
>>>>>> type: poly
>>>>>> Space in 1 variables with 1 components, size 2
>>>>>> Polynomial space of degree 1
>>>>>> PetscDualSpace Object: Q1 (mech_) 1 MPI process
>>>>>> type: sum
>>>>>> Dual space with 2 components, size 8
>>>>>> Sum dual space of 2 concatenated subspaces (all identical)
>>>>>> PetscDualSpace Object: Q1 1 MPI process
>>>>>> type: lagrange
>>>>>> Dual space with 1 components, size 4
>>>>>> Continuous tensor Lagrange dual space
>>>>>> Quadrature on a quadrilateral of order 3 on 4 points (dim 2)
>>>>>> Field p FEM 3 components (implicit) (Nq 4 Nqc 1) 1-jet
>>>>>>
>>>>>
>>>>> 1. Why does pressure have 3 components in 2D?
>>>>>
>>>>>> PetscFE Object: p (pres_) 1 MPI process
>>>>>> type: vector
>>>>>> Vector Finite Element in 2 dimensions with 3 components
>>>>>> PetscSpace Object: Q0 (pres_) 1 MPI process
>>>>>> type: sum
>>>>>> Space in 2 variables with 3 components, size 3
>>>>>> Sum space of 3 concatenated subspaces (all identical)
>>>>>> PetscSpace Object: Q0 (pres_sumcomp_) 1 MPI process
>>>>>> type: tensor
>>>>>> Space in 2 variables with 1 components, size 1
>>>>>> Tensor space of 2 subspaces (all identical)
>>>>>> PetscSpace Object: sum component tensor component
>>>>>> (pres_sumcomp_tensorcomp_) 1 MPI process
>>>>>> type: poly
>>>>>> Space in 1 variables with 1 components, size 1
>>>>>> Polynomial space of degree 0
>>>>>> PetscDualSpace Object: Q0 (pres_) 1 MPI process
>>>>>> type: sum
>>>>>> Dual space with 3 components, size 3
>>>>>> Sum dual space of 3 concatenated subspaces (all identical)
>>>>>> PetscDualSpace Object: Q0 1 MPI process
>>>>>> type: lagrange
>>>>>> Dual space with 1 components, size 1
>>>>>> Discontinuous tensor Lagrange dual space
>>>>>> Quadrature on a quadrilateral of order 3 on 4 points (dim 2)
>>>>>> Weak Form System with 2 fields
>>>>>>
>>>>>> using as the second field (dim = 2, nc = 3, prefix = "pres") and
>>>>>> setting the FE object name to "p".
>>>>>>
>>>>>> The entry "cell total dim 10" agrees with the output of
>>>>>> PetscFEGetTotalDimension(); "comp = 5" I assume is 2 (u) + 3 (p)
>>>>>>
>>>>>> However, the closure of a Vec is still 22.
>>>>>>
>>>>>
>>>>> 2. Did you look at the incompressible example SNES ex69? It sets up
>>>>> this exact element.
>>>>>
>>>>> 3. Please send me that code that sets up your DM. It sounds like
>>>>> somehow you have a copy of your fields.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Matt
>>>>>
>>>>>> On Tuesday, May 5th, 2026 at 1:58 PM, Matthew Knepley <
>>>>>> knepley at gmail.com> wrote:
>>>>>>
>>>>>> On Tue, May 5, 2026 at 9:06 AM Noam T. via petsc-users <
>>>>>> petsc-users at mcs.anl.gov> wrote:
>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> I am trying to work with a "mixed" FE discretization, where besides
>>>>>>> the usual displacements DoF in nodes, there is an additional field (e.g.
>>>>>>> pressure) that is also part of the system. This additional field has a
>>>>>>> certain number of additional dof : p0, p1, p2...
>>>>>>>
>>>>>>> Looking at example 77 (
>>>>>>> https://urldefense.us/v3/__https://petsc.org/release/src/snes/tutorials/ex77.c.html__;!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMov1NT81$
>>>>>>> <https://urldefense.us/v3/__https://petsc.org/release/src/snes/tutorials/ex77.c.html__;!!G_uCfscf7eWS!aZNOxZZeoHYqe6lRZV0wHMVVTu3YIEfc1Sr-dca7xiGVfG3enULFD4_g6_fxWIa7A_Cu9LcXU-MuxRj4sOwDRyWqvsdGdrEd$>)
>>>>>>> this seems to be handled with an additional field, added to the DM. I've
>>>>>>> tried so, but then I am getting from the DM arrays whose size/contents are
>>>>>>> not what I expected.
>>>>>>>
>>>>>>> For example, a four-noded Q1 element (PetscFE created with a 2x2
>>>>>>> Gauss rule for quadrature), with just one field, a call to
>>>>>>> DMPlexGetVecClosure() gives me an array with 8 entries (say, the
>>>>>>> coordinates of the initial mesh): x = x0, y0, .... x3, y3
>>>>>>>
>>>>>>> Then add the new field:
>>>>>>>
>>>>>>> PetscFECreateDefault(..., nc = 3, ..., p_FE) /* not sure about the
>>>>>>> value of nc here */
>>>>>>> DMAddField(dm, ..., p_FE)
>>>>>>>
>>>>>>> The total dimension, from PetscDSGetTotalDimension(), is now 11 (8
>>>>>>> + 3). This results in a closure of size 22.
>>>>>>>
>>>>>>
>>>>>> That is wrong. Are you sure about 22?
>>>>>>
>>>>>>> However, what I am looking for is a closure of size 8 + 3 i.e. the
>>>>>>> original 8 DoF at the nodes, plus exactly 3 DoF (for the cell, so to speak)
>>>>>>> p0, p1, p2, so that in a system with "block" matrices of the form
>>>>>>>
>>>>>>> [K_uu, K_up | K_pu, K_pp] { u | p } = RHS
>>>>>>>
>>>>>>> the unknowns {p} has size 3 per cell. Is this possible? I tried some
>>>>>>> combinations of dim / nc for the new PetscFE, but when creating the DM
>>>>>>> section I get errors e.g.
>>>>>>>
>>>>>>
>>>>>> This is what you should get. I definitely have examples that do this.
>>>>>> For example, here is Q1-P0 (I think that is what you are suggesting) for
>>>>>> incompressible Stokes
>>>>>>
>>>>>>
>>>>>> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/snes/tutorials/ex69.c?ref_type=heads*L3454__;Iw!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMvSX71k5$
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Matt
>>>>>>
>>>>>>> "point X has a number of DoF not divisible by 2 field components"
>>>>>>>
>>>>>>> Is this a hint that I should have 3 x dim new DoF, and simply not
>>>>>>> deal with entries that I don't need? Or I am not setting up the section
>>>>>>> properly (works with just one field)?
>>>>>>>
>>>>>>> Thank you,
>>>>>>> Noam.
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> What most experimenters take for granted before they begin their
>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>> experiments lead.
>>>>>> -- Norbert Wiener
>>>>>>
>>>>>> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
>>>>>> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> What most experimenters take for granted before they begin their
>>>>> experiments is infinitely more interesting than any results to which their
>>>>> experiments lead.
>>>>> -- Norbert Wiener
>>>>>
>>>>> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
>>>>> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> What most experimenters take for granted before they begin their
>>>> experiments is infinitely more interesting than any results to which their
>>>> experiments lead.
>>>> -- Norbert Wiener
>>>>
>>>> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
>>>> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>>>>
>>>>
>>>>
>>>
>>> --
>>> What most experimenters take for granted before they begin their
>>> experiments is infinitely more interesting than any results to which their
>>> experiments lead.
>>> -- Norbert Wiener
>>>
>>> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
>>> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>>>
>>>
>>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
>> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>>
>>
>>
>>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$
> <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
>
>
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMtW45maR$ <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!cP9aUMsk0h6B0TP8LN-o6KeS5DUoqycfFJOuLYmU4gSo5kx4ivqdhEodvmnZ16VQW3AsR4qmMxVoMob7Dulh$ >
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