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
The dense Jacobian arrays `J0_dense` and `J1_dense` are now zeroed only once before the vertex loop. Inside the loop, only the entries that were actually used are zeroed out after being added to the sparse Jacobian, allowing for efficient reuse of the dense arrays across all vertices.
PiperOrigin-RevId: 860799056
Change-Id: Ia61daae5eeb2f4dbc0c5d8c0064622a881e92b7a
This is a more general API in preparation of a higher interpolation order
PiperOrigin-RevId: 820174741
Change-Id: I81bd52ab44e0485d72579e21d1c8a48a1b35ec3f
This is a no-op "prefactor" of `mj_crb` to reduce the number of lines changed in the upcoming sleeping CL. The main change here is that `mj_crb` now avoids accessing the model and data pointer repeatedly, but instead has the input and output pointers explicitly declared as local variables. A benchmark test found a healthy **14% perf bump** due to two changes:
- Adding `restrict` to `mju_mulInertVec`
- The function-local pointers.
Adding `restrict` to the local pointers had no effect. Note that `mj_crb` is not a particularly expensive function so these speed bumps are not significant per se, but rather indicative of possible future gains with these techniques.
```
Benchmark Time(ns) CPU(ns) Iterations
---------------------------------------------------------------
ORGINAL BASELINE
BM_CRB_BASELINE_mean 4325 4348 993200 230.052k items/s
BASELINE + RESTRICT
BM_CRB_BASELINE_mean 4057 4090 1186150 244.573k items/s
LOCAL POINTERS + RESTRICT
BM_CRB_mean 3772 3800 1001750 263.209k items/s
```
PiperOrigin-RevId: 815798225
Change-Id: Iffdf57b544e8e10562807c617f73ca4ccd1c614f
Notes:
- Currently always uses dense math, even for sparse models. This should be easy to change in the future.
- Does not support geom wrapping. This is possible but harder, requires derivatives of mju_wrap.
PiperOrigin-RevId: 740378741
Change-Id: Id39ef2c4bfbb7ee11ec33c97d7d83140441cdab2
These flexes use only 24 DOFs (3 per vertex of the bounding box), while colliding with the full high resolution mesh.
On an 8x8x8 cube, the performance using DOFs at all vertices is
```
Simulation time : 18.74 s
Steps per second : 533
Realtime factor : 0.53 x
Time per step : 1874.4 µs
Contacts per step : 114.88
Constraints per step : 3322.51
Degrees of freedom : 1536
```
With the new implementation, it is the following:
```
Simulation time : 1.82 s
Steps per second : 5507
Realtime factor : 5.51 x
Time per step : 181.6 µs
Contacts per step : 38.84
Constraints per step : 155.36
Degrees of freedom : 24
```
PiperOrigin-RevId: 721008829
Change-Id: I833df027527db578d86667cc4b24295bcf6f7d22
Alessio Quaglino