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Enhancement-886: newtrunc and its three tolerances say they have no effect, and what is used instead — ltereltol, lteabstol and ltetrtol were taken without a word

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@javaNoviceProgrammer javaNoviceProgrammer released this 13 Oct 05:19
· 5 commits to main since this release
Enhancement-886_ltenote
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Enhancement-886: newtrunc and its three tolerances say they have no effect, and what is used instead — ltereltol, lteabstol and ltetrtol were taken without a word

Scope: N4 of the
transient stress campaign of 2026-10-12.

ngspice: spicelib/analysis/cktsopt.c, CKTsetOpt: OPT_LTERELTOL, OPT_LTEABSTOL and
OPT_LTETRTOL warn in a build without PREDICTOR, and OPT_NEWTRUNC's warning says what runs
instead. Stock options.

examples/transnotes_examples/ (new, shared with E-885,
E-887 and E-888). ngspice only.

Suites:

  • transnotes_examples: [4] is this enhancement's, 11 of 11
    per solver. On the E-883 binaries [4] fails.
  • inputguard passes.
  • The full sweep: 587 of 587.

What was wrong

.option newtrunc selects a truncation estimate from node voltages: the difference between a
predictor and the corrector. The predictor is compiled in only by --enable-predictor
(PREDICTOR), which also changes every device's Newton start, and this build, like stock
ngspice's default, does not have it. newtrunc said so:

Warning: Option 'newtrunc' ignored,
    compilation with preprocessor flag 'PREDICTOR' is required.

Its three tolerances, ltereltol, lteabstol and ltetrtol, were stored and read by nothing,
and said nothing. Family A's newtrunc rows were trap rows.

The change

Warning -- Option newtrunc is ignored: the voltage-based truncation estimate needs the predictor, which this build does not have (ngspice configured with --enable-predictor has it). The estimate from the charges, set by reltol, abstol, chgtol and trtol, is used.

Warning -- Option ltereltol has no effect: it is a tolerance of newtrunc's voltage-based truncation estimate, which this build does not have (see newtrunc). The estimate from the charges, set by reltol, abstol, chgtol and trtol, is used.

lteabstol and ltetrtol say the same. newtrunc=0 and a deck without them say nothing. In a
build with PREDICTOR nothing changes.

The checks

transnotes_examples:

  • [4] newtrunc says it is ignored and that the charge estimate is used; ltereltol,
    lteabstol and ltetrtol each say they have no effect; a deck without them prints neither.

Write-up: enhancements_doc/Enhancement-886.md

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