Method Fidelity

March 30, 2026 ยท View on GitHub

This page explains how Surge uses method labels in public documentation. The goal is simple: when Surge says a workflow is a full solve, an approximation, or a screening method, those terms should mean something consistent.

Method Labels

LabelMeaning
Reference-equationA solver for the stated mathematical formulation within its stated assumptions.
ApproximationA simplified model used for speed, scale, or tractability.
HeuristicA ranking, screening, or stress-indicator method that is useful in practice but is not presented as a proof or certificate.
Empirical standardA method defined by an external standard, rule set, or regression-based practice rather than first-principles network equations alone.
ExperimentalPresent and usable, but not presented as the primary production path for that study type.
Supporting infrastructureData models, parsers, sparse algebra, bindings, and similar implementation layers rather than study methods.

Current Method Map

AC Power Flow

  • Newton-Raphson is the primary reference-equation AC power flow method.
  • Fast Decoupled Power Flow is an approximation.

DC Power Flow And Sensitivities

  • DC power flow is a reference-equation solve of the DC approximation itself.
  • PTDF, LODF, and related linear sensitivity workflows are approximations relative to full nonlinear AC behavior.

Contingency Analysis

  • Post-contingency AC re-solve is the nonlinear validation step and should be read as the reference-equation path.
  • LODF and FDPF screening layers are approximations.
  • Local voltage-stress indicators are heuristics.

OPF

  • DC-OPF is an approximation.
  • AC-OPF is a reference-equation solve for the stated nonlinear optimization model.
  • Convex relaxations and screening variants should be read according to their own model assumptions, not as aliases for AC-OPF.

HVDC

  • Supported HVDC workflows model converter and network behavior directly, but the current public workflows still include sequential or block-iterative coupling choices.
  • Those coupling choices should not be described as a monolithic simultaneous Newton solve unless the implementation actually does that.

Transfer Capability

  • PTDF-, DFAX-, and screening-led transfer workflows are approximations.
  • AC confirmation and stability-limited follow-on steps are the higher-fidelity parts of the workflow.

I/O, Topology, Sparse Algebra, CLI, And Python Bindings

  • These are supporting infrastructure, not study methods.

How To Read Public Docs

When Surge documentation describes a workflow:

  • reference-equation means the implementation is intended to solve the stated formulation, not a looser screening proxy.
  • approximation means the workflow is simplified by design and should be interpreted within that model's limits.
  • heuristic means the result can guide prioritization or screening, but is not presented as a formal guarantee.

Validation And Evidence

Public evidence claims should point to maintained tests in this repository or to real, maintained artifacts in surge-bench.