An extracted resistance or inductance looks unphysical

Check what the fitted model represents

The extracted branch values are fitted to the specified circuit model. A missing branch contribution or mutual coupling can force an otherwise useful field solution into an inadequate lumped model. A negative value is not automatically a harmless numerical artifact.

A historical support case attributed a negative resistance to an incomplete bias-network model. That diagnosis does not establish the cause of a new negative value.

Review the result

1. Check port directions and the intended circuit topology against the physical layout.
2. Include the branch and coupling contributions required by that model; avoid changing physical parameters merely to make a value positive.
3. Inspect SVD rank, unknown count, condition number and residuals using the matching manual. A small voltage residual alone does not prove every element value is accurate.
4. Repeat a controlled mesh/refinement check and compare a simpler model before trusting the result.

When to escalate

Provide a minimal model and the relevant solution diagnostics privately. Treat unexpected values as unresolved until the circuit and field model explain them.

Compare with the design

Aim for low reported relative error in the model fit. The owner has not specified a new numerical cutoff for SVD or GMRES residuals.

For a meaningful nonzero design inductance, use 100 × abs(L_extracted − L_design) / abs(L_design) to compare the values. The general design target is below 10% deviation; below 5% is preferred.

Design agreement, model-fit residuals and solver convergence answer different questions. Check the physical model and refinement behaviour as well; these percentages are not universal solver-error or regression tolerances.