QF Solver 0.2.5a0 G04 External Branch Diagnostic¶
Decision Boundary¶
This document resolves the discrepancy between the internal two-element TET4
arc-length path and the historical Code_Aster replay. It does not close
025-G04, change any acceptance criterion, or make an arc-length production
claim.
| Provenance item | Value |
|---|---|
| Original QF numerical source | 067859c1db8416758f82bc339cc5b2db4bcbaf63 |
| Historical Owner evidence | 8fdbd500e52a2c23174f66c68e19ecfaa57be0c5 |
| Authoritative corrected-run source | results/vnv_0_2_5/g04_latest/evidence_manifest.json |
| Gate status | OPEN |
| Contract lowered | NO |
Strict Configuration Comparison¶
| Parameter | QF Solver | Historical Code_Aster deck | Corrected Code_Aster deck | Impact |
|---|---|---|---|---|
| Geometry | five unperturbed nodes; apex (0, 0, 0.25) |
same | same | match |
| Connectivity | N1-N3-N4-N5, N2-N4-N3-N5 |
same | same | match |
| Material | E=100, nu=0.3 |
same | same | match in the bounded elastic case |
| Kinematics | Total-Lagrangian, Green-Lagrange / second Piola | ELAS, GREEN_LAGRANGE |
same | bounded formulation match |
| Supports | N1/N2 fixed; crown UY=0 |
same | same | match |
| Physical load | QF reference +1/3 with target factor -1: downward |
FZ=+1/3: upward |
FZ=-1/3: downward |
historical mismatch resolved |
| Control output | apex node N5 UZ (global DOF 14) |
mean CROWN/DZ |
APEX/DZ |
historical mismatch resolved |
| Continuation window | 80 QF steps through |u_apex|=0.94194 |
0..100, 800 intervals |
0..0.96, 160 intervals |
corrected window covers the QF branch |
| Arc constraint | QF augmented displacement/load norm | Code_Aster LONG_ARC displacement control |
same | compare equilibrium points by apex displacement |
The values are a dimensionless/scaled numerical benchmark. No physical unit validation is claimed.
Diagnostic Result¶
The corrected Code_Aster run gives one turn at the same branch location as QF Solver. Interpolating Code_Aster's reaction-derived load factor on QF's absolute apex displacement gives:
| Metric | Result |
|---|---|
| QF turning point | u=0.8933769433, lambda=-0.03732654177 |
| Code_Aster turning point | u=0.8940000000, lambda=-0.03732647828 |
| Absolute turning-load difference | 6.3485e-08 |
| Maximum branch load-factor difference | 4.8719e-07 |
| RMS branch load-factor difference | 2.0730e-07 |
| Peak-normalized maximum difference | 1.3052e-05 |
QF's reduced tangent is symmetric to numerical precision. Its smallest
eigenvalue crosses from +1.1649e-03 at step 75 to -3.3334e-06 at step 76,
then stays negative on the post-limit branch. The reassembled free residual
near the turn is below 5e-13, and det(F) remains positive (>=0.4414 over
the recorded path). This supports a physical limit-point interpretation within
the bounded two-element model.
Classification¶
DIAGNOSIS = B - CODE_ASTER_PATH_FOLLOWING_CONFIGURATION
ROOT CAUSE = opposite physical load direction plus unmatched control observable
and continuation window in the historical deck
QF_MODEL_VALID = YES, bounded numerical correlation only
CODE_ASTER_MODEL_VALID = YES after deck correction
PUBLISHED_REFERENCE = NOT_IDENTIFIED
CODE_CHANGE_REQUIRED = NO
G04 STATUS = OPEN
The exact two-element configuration has no linked published FEM source in the
repository, and no exact public reference was identified for it. The Code_Aster
manual supports LONG_ARC as a continuation method but is not a published
reference for this particular geometry or branch.
Remaining G04 Blockers¶
- Link and reproduce an exact published FEM snap-through branch reference, or formally replace this custom benchmark through the requirements process.
- Run the required coarse/medium/fine/refined branch study only after the benchmark reference is approved.
No mesh study was run during this diagnostic. The corrected Code_Aster branch removes the historical external-deviation blocker but does not close the gate.