Line Filtering

Line Filtering#

For wide wavelength coverage (or many segments), using the full line list in every segment is expensive. PySME provides dynamic line filtering to keep only relevant lines per segment (see Jian et al. in prep).

Core Options#

Use linelist_mode and line_select_method together in synthesis or solve:

  • "all": use all lines (default).

  • "dynamic": filter lines by precomputed line properties (recommended for long spectra).

  • "auto": legacy alias of "dynamic" (deprecated).

  • line_select_method="internal": no external preselection metadata.

  • line_select_method="cdr": use central_depth + line_range_*.

  • line_select_method="almax": use almax_ratio + line_range_*.

How Dynamic Filtering Works#

When linelist_mode="dynamic":

  1. PySME ensures line metadata exists for the selected method.

    • cdr: central_depth, line_range_s, line_range_e

    • almax: almax_ratio, line_range_s, line_range_e

  2. If metadata is missing or stale, PySME updates it automatically.

  3. For each segment, PySME keeps lines that overlap the segment range (with broadening margin) and pass a strength threshold.

  4. Only this reduced line subset is sent to SMElib for that segment.

This can significantly reduce runtime for long or segmented spectra.

Main Controls#

  • Shared controls:

    • sme.line_select_method: internal | cdr | almax

    • sme.line_select_parallel: enable/disable parallel metadata update

    • sme.line_select_n_jobs: number of worker processes

    • sme.line_select_chunk_size: chunk size for metadata update

    • sme.line_select_recompute: if_stale | always | never

    • sme.line_select_stale_thres: stale thresholds for model changes

  • CDR method controls:

    • sme.line_select_cdr_strength_thres

    • sme.line_select_cdr_bin_width

    • line_precompute_database / cdr_create (function args)

  • ALMAX method controls:

    • sme.line_select_almax_threshold

    • sme.line_select_almax_use_bins

    • sme.line_select_almax_bin_width

line_precompute_database is a shared on-disk cache for both cdr and almax. Cache entries are isolated by (method, linelist_hash, stellar params), so one folder can safely store multiple linelists and both methods together. Legacy cdr_database is still accepted as an alias.

ALMAX strong-line rule#

  • line_select_almax_use_bins=False:

    • strong = (almax_ratio >= line_select_almax_threshold)

  • line_select_almax_use_bins=True:

    • strong = flag_strong_lines_by_bins(wl, almax_ratio, threshold=line_select_almax_threshold, bin_width=line_select_almax_bin_width)

line_select_almax_threshold is the single ALMAX threshold parameter for both rules. If it is None, it falls back to sme.accrt (legacy-compatible behavior).

Example 1: Dynamic Filtering in Synthesis (CDR)#

from pysme.synthesize import Synthesizer, synthesize_spectrum

synth = Synthesizer()
sme = synth.update_cdr(sme)              # populate central_depth / line_range_* once
sme.line_select_method = "cdr"
sme.line_select_cdr_strength_thres = 0.02

sme = synthesize_spectrum(sme, linelist_mode="dynamic")

Example 2: Dynamic Filtering in Synthesis (ALMAX)#

from pysme.synthesize import synthesize_spectrum

sme.line_select_method = "almax"
sme.line_select_almax_threshold = sme.accrt
sme.line_select_almax_use_bins = True
sme.line_select_almax_bin_width = 0.2

sme = synthesize_spectrum(sme, linelist_mode="dynamic")

Example 3: Dynamic Filtering in Solve#

from pysme.solve import solve

fit = ["teff", "logg", "monh", "vmic"]
sme.line_select_method = "almax"
sme.line_select_almax_use_bins = True

sme = solve(
    sme,
    fit,
    linelist_mode="dynamic",
    line_precompute_database="path/to/line_precompute_db",
    cdr_create=False,                     # set True to force regeneration
)

Practical Guidance#

  • Start with line_select_method="cdr" for continuity with existing CDR workflows.

  • For ALMAX, start with line_select_almax_threshold = sme.accrt.

  • Enable line_select_almax_use_bins=True when you want bin-wise cumulative pruning.

  • Use "all" for short, narrow windows where filtering overhead may not help.

  • Use "dynamic" for wide ranges or many segments.

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