The coordinates for flex interpolation are now computed using the absolute values of the vertex weights. The sign of the first vertex weight is then applied to the resulting barycentric weights. This correctly handles cases where the flex is both the first and the second entity in the contact pair.
PiperOrigin-RevId: 913590928
Change-Id: I970b35fba3d209e13b5b33bb5f945e3c6a43d487
- Compute efc_J_rowsuper incrementally in mj_addConstraint instead of post-hoc via mju_superSparse.
- Better exploitation of supernodes in A matrix pipeline: precount and fill skip redundant chain traversals for supernode rows.
- Redundant B_rowsuper computation via mju_superSparse is eliminated (indentical to efc_J_rowsuper).
PiperOrigin-RevId: 910787825
Change-Id: I6eda9996659602b7051ee1090aeedb862603c84e
When elastic2d="stretch" is set on an interpolated flexcomp, treat the bounding box boundary as membrane elements rather than volumetric cells. This computes plane-stress stiffness over the boundary faces and updates the runtime force/derivative kernels accordingly.
Interior vertex tracking (moving vertices that follow the deforming shell) is not yet implemented so all mesh vertices need to be on the bounding box surface or the background grid should have no interior nodes (i.e. cellcount should be 1 on at least one axis).
PiperOrigin-RevId: 907654080
Change-Id: I51b90e2f6a1d1b036f9604e42de20e377dc5d3f9
Do not allow a mix of `elastic2d != none` with `dof = trilinear` since the latter assumes 3d elasticity.
Also, do not assume that `flex_interp > 0` in the engine. This will enable to use, e.g., `flex_interp = -1` to mean a linear surface finite element instead of a 3d finite element which is currently identified with `flex_interp = 1`.
PiperOrigin-RevId: 903852035
Change-Id: Ia6290b4a05e9e510ffb7f36d141cd525b40d3110
This change introduces an optimization for flexcomp objects defined by a mesh. It identifies grid cells that do not contain any mesh vertices and marks them as empty. Nodes that are exclusively part of empty cells are pinned, preventing them from moving. Stiffness computations are skipped for empty cells, reducing computational cost. The total mass is now distributed only among the non-pinned nodes.
PiperOrigin-RevId: 902565735
Change-Id: Id0a9a685536d5e18a3e42124a25ab08ff3a918f2
Combine sparse vectors in-place by first counting total `nnz` and then working backwards from the end. This removes the need for temporary buffers in `mju_combineSparse` and its callers and speeds up the function by ~10%.
PiperOrigin-RevId: 902530210
Change-Id: I4f48c327103552ab968d3915399c6067367bec9f
This provides a reduction from 26 to 18 constraints for trilinear and from 162 to 75 for quadratic. The assembly of the constraints becomes trivial. In total the speedup for a trilinear 3x3x3 grid is about 3x.
PiperOrigin-RevId: 902502398
Change-Id: I764772c7adef78da5a644f64701f842d36e4b543
Each mjEQ_FLEXSTRAIN equality now represents a single cell within a flex. This allows for more efficient sparse Jacobian computation by only considering the degrees of freedom of the nodes within each specific cell. This change gives a speedup of about 10x on a 3x3x3 model.
PiperOrigin-RevId: 902164069
Change-Id: I78eedf1d5cf39b8989fe9863c22d164922fc0efb
This change introduces a `flex_cellcount` field to `mjModel` to specify the number of cells in each dimension for interpolated flexes. The stiffness computation, passive force calculation, and Jacobian derivatives are updated to operate on a per-cell basis, significantly improving performance by localizing computations to the nodes within each cell.
PiperOrigin-RevId: 901216393
Change-Id: Ic23132e609de11e71bb7fef8d1f139daad2ec264
The `grad` parameter in `volumetric_dSdx` and `invariant_dSdx` is not modified, but the `const` qualifier was inconsistent with how the array was being passed, requiring an unnecessary cast. Removing the `const` simplifies the function signatures and calls.
PiperOrigin-RevId: 884598322
Change-Id: Icac8071aa8e838057dd39c979c23a4f47e1dc22d
This change improves trilinear flex elements by using reduced integration for volumetric quantities (strain trace and volume ratio) at the element center, while adding full integration for shear components at 8 Gauss points and removing the second strain invariant from the constraints, which is negligible for small strains. This reduced integration "B-bar" technique is standard in finite element analysis and prevents artificial stiffness that can occur when low-order elements are nearly incompressible. The constraint count per trilinear element changes from 24 to 26 compared to using invariants. For quadratic elements, the full 27 quadrature point are used resulting in 162 constraints.
PiperOrigin-RevId: 884570752
Change-Id: Ib74ece8f4712c2c81fbfd784524fcac52a2c80e5
For each contact point, we used to first compute the vertex weights on a triangle and then add a contact point per vertex using the flex interpolation (trilinear or quadratic), obtaining the total weight by multiplying the vertex weight and the basis function value at that vertex. After this change, each contact point is added directly by evaluating the basis function directly a the point.
PiperOrigin-RevId: 834218909
Change-Id: Ic0fdb03fc0ef5478798c293df99204fd33116fd1
This ensures that at e.g. the barycenter of the triangle each vertex has weight 1/3, as one would expect with barycentric coordinates, rather than 1/sqrt(3). This makes it consistent to the finite element interpolation used in the passive elastic forces.
PiperOrigin-RevId: 823458736
Change-Id: Ia5c02cba186a80612de38402f791695c33e991ab
This is a more general API in preparation of a higher interpolation order
PiperOrigin-RevId: 820174741
Change-Id: I81bd52ab44e0485d72579e21d1c8a48a1b35ec3f
Yuval Tassa