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Adjoint field dual is silently zero for a field that enters through a Dirichlet datum #787
Description
solver.gradient(misfit, fields=[f]) returns the dual on a field the residual reads. A field that enters only through an essential datum, u|Γ = f (a prescribed velocity field on a wall, an observed temperature used as a boundary value), is not seen: the field route scans the residual, not the boundary data, so the dual comes back zero and nothing says so. The scalar-parameter case was #762; this is its field counterpart.
The term is the same reaction, [(Kᵀμ)_Γ + (∂J/∂u)_Γ] restricted to the constrained rows and mapped onto the field's own nodes (a projection when the spaces differ). Until it is built, a field found in an essential datum should refuse rather than return zero.
Branch feature/discrete-adjoint, PR #744.
Activity
lmoresi commentedon Oct 7, 2026
Not reproducible on
development(7c9cbbfd) — the adjoint API is not there:Only scattered references remain (one line in
petsc_generic_snes_solvers.pyx, five inmcp/__init__.py, eight intranscript_query.py), not the implementation. So this defect lives in unmerged work —feature/discrete-adjoint(#744, currently conflicting and red),feature/adjoint-rotated-bc(#751, based on #744), orscratch/adjoint-merge.That is why it has sat untouched: there is nothing on the main line to fix. It is not
fixed-in-PR— the opposite. It has to be fixed on the branch before that branch lands, or it lands with the defect.Checked in the untouched-issue triage. Blocked behind #744, which needs its conflicts resolved and a CI re-run (its red check is
test_1063_constrained_traction, whose timeout #814 addressed when it merged on 2026-10-06).