ngspice

ngspice is Monata’s current native simulator target. Monata renders native monata.netlist.Circuit objects to ngspice-compatible text and executes them through a user-installed ngspice runtime.

Monata has two ngspice runner paths:

• ngspice-subprocess is the stable default. It runs a local ngspice executable through a subprocess.

• ngspice-shared is the same-simulator shared-library path. It loads a local libngspice shared library through Monata’s default Python FFI dependency.

The current ngspice backend support covers deterministic DC sweep, transient, AC, operating-point, and noise runs. Unsupported analyses return SimResult(status="failed") with an explicit reason until their native implementations are added.

Runtime Contract

• The public Monata package does not bundle ngspice.

• The backend resolves a local ngspice executable from PATH or CONDA_PREFIX/bin.

• The shared-library backend resolves a local libngspice library at runtime; Monata does not ship that library.

• Internal packaged environments may install ngspice as a separate package, but public users should install or build the tool in their own environment.

• DC, transient, and AC results are written with ngspice wrdata using a single sweep scale.

• DC, transient, AC, and operating-point tasks must provide explicit output_names; Monata does not infer output vectors from the netlist.

• Noise tasks use NoiseSpec.output_node and NoiseSpec.input_source as the explicit request. SimTask.output_names must be empty for noise.

• DC and transient outputs are emitted as v(name).

• AC outputs are emitted as mag(v(name)).

• Operating-point outputs are emitted as one-row arrays parsed from print v(name).

• Noise outputs are parsed from ngspice noise1/noise2 print output as onoise_spectrum, inoise_spectrum, and totals metadata.

• OSDI libraries in SimTask.osdi_paths are loaded with pre_osdi before the analysis command.

• Plain .include model cards can be emitted by the native netlist renderer.

Distribution and License Boundary

The ngspice source tree contains a primary modified-BSD license plus specific subtree exceptions for components such as KLU, OSDI, numparam, XSPICE table code models, and other bundled source. Public Monata packages avoid carrying that native code by treating ngspice as an external runtime dependency.

When users or organizations build ngspice from source, they should keep the upstream license files and notices with the resulting installation. Monata documentation may provide build steps, but it does not redistribute the built ngspice executable, libngspice, XSPICE .cm binaries, or compiled OSDI artifacts.

Supported Task Inputs

Input	Current behavior
DCSpec	Executes dc <source> <start> <stop> <step>
TranSpec	Executes tran <step> <stop> <start>
ACSpec	Executes `ac <dec
OPSpec	Executes op, then parses requested v(name) values
NoiseSpec	Executes noise v(output_node) input_source dec <points> <start> <stop>
output_names	Required for DC/Tran/AC/OP; must be empty for Noise
osdi_paths	Existing files are loaded with pre_osdi
param_overrides	Simple .param names are emitted after existing params; element.parameter targets mutate native elements
corner temperature	Emits .temp <temperature>
corner voltage	Mutates matching voltage sources through source.V overrides
corner model file	Emits .include "<model_file>"

Explicit Limitations

The backend fails explicitly instead of silently ignoring unsupported inputs:

Input	Failure reason
unsupported analysis type	unsupported_analysis
empty output_names for DC/Tran/AC/OP	no_outputs_requested
non-empty output_names for Noise	invalid_task
unsafe output names, OSDI paths, or analysis command fields	invalid_task
missing OSDI or corner model file	model_missing
missing or unsupported parameter/source override targets	unsupported_param_overrides
process or model-deck corner without a concrete model file	unsupported_corner

Advanced ngspice work such as binary rawfile parsing, richer noise output contracts, and richer model-deck projection is tracked in the maintainer Monata Roadmap TODO.