SYSTEM_REQUIREMENTS.md memory model is stale: attributes the 29 GB calibration peak to a dense-row vstack the compiler no longer does

Summary

SYSTEM_REQUIREMENTS.md explains the ~29 GB calibration peak with a mechanism the code no longer has, so its capacity-planning formula should not be trusted until remeasured.

Evidence

SYSTEM_REQUIREMENTS.md:118-128 states:

peak RAM is set by the compile step ... build_constraint_matrix materializes one dense row per target into a Python list and np.vstacks them before compressing to CSR, so peak RAM ≈ 2 × n_targets × n_records × 8 bytes (the row list + the vstack copy)

Current matrix compilation (packages/populace-calibrate/src/populace/calibrate/matrix.py:198-260) materializes one dense row at a time, immediately reduces it to its nonzero indices/data parts, and builds CSR directly — there is no retained dense-row list and no np.vstack copy. The documented 2×-dense formula (and the 300k-record / 6,288-target ≈ 28-29 GB ceiling derived from it) describes the old implementation.

Peak memory today is more plausibly set elsewhere (six pandas entity-table copies at H5 load, full Microsimulation construction during target materialization, CSR + torch tensors during solve) — which matters for machine sizing on Build J-class runs.

Acceptance criteria

• Remeasure peak RSS of a current-main calibration at production scale (or a scaled measurement with the scaling law stated), and update the SYSTEM_REQUIREMENTS.md formula and table to the observed mechanism.
• The dense-row/np.vstack explanation is removed or explicitly marked historical.

Cross-links

• #299 (the OOM history that motivated the document)
• #285 (production-scale sweep runs that could produce the measurement for free)

Surfaced by an external architecture review (Codex/gpt-5.6-sol, 2026-07-09); citations independently verified.

Read SYSTEM_REQUIREMENTS.md:118-128 alongside packages/populace-calibrate/src/populace/calibrate/matrix.py:198-260, then measure peak RSS for a current-main calibration at production scale or with a stated scaling law. Account for the H5 entity-table copies, Microsimulation construction, and CSR plus torch tensors; update the formula and table to match the observed mechanism and remove or mark the dense-row explanation historical.