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rugnux: report anomalous signal-to-noise SigAno (stats table + mmCIF)

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Compute SigAno = <|I(+)-I(-)|>/<sigma(I(+)-I(-))> per report shell and overall
from the full-multiplicity I(+)/I(-) Bijvoet split, store it on
MergeStatisticsShell, and surface it in the console merge-statistics table (new
SigAno column) and the mmCIF via the standard wwPDB PDBx items
_reflns.pdbx_absDiff_over_sigma_anomalous (overall) and
_reflns_shell.pdbx_absDiff_over_sigma_anomalous (per shell) - the dictionary's
home for this quantity, so no jfjoch_ local item is needed (unlike ISa).

SigAno approaches ~0.8 for pure noise and rises above 1 with real anomalous
signal. A half-set anomalous CC is deliberately not used: its two half estimates
are complementary partitions of one observation pool (dI0 + dI1 = 2*dI_full), so
differencing the two Bijvoet hands cancels the large common intensity that keeps
CC1/2 non-negative and, once the anomalous SNR per half drops below 1, drives the
correlation towards -1 rather than 0 - misrepresenting a weak-but-real signal.

Emitted only when an anomalous split was made (has_anom guard), so a non-anomalous
merge keeps its stats block and shell-loop columns byte-for-byte. Export-neutral:
the I(+)/I(-)/IMEAN accumulation is unchanged. On low-energy S-SAD test data SigAno
tracks XDS (13 keV null ~0.89, 6 keV ~1.44, 5 keV ~1.5-1.7) and never goes
spuriously negative.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
leonarski_f
2026-07-17 20:54:03 +02:00
co-authored by Claude Opus 4.8
parent 1b5eb80ba4
commit 7fe12773de
4 changed files with 45 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
image_analysis/WriteReflections.cpp
+12 -1
View File
@@ -135,6 +135,9 @@ void WriteMmcifReflections(const std::vector<MergedReflection> &reflections,
? 100.0 * static_cast<double>(s.unique_reflections) / s.possible_unique_reflections : 0.0; };
if (!statistics.shells.empty()) {
const auto &ov = statistics.overall;
// Anomalous signal-to-noise (SigAno) is written only when an anomalous split was made, so a
// non-anomalous merge keeps its previous stats block / shell-loop columns unchanged.
const bool has_anom = std::isfinite(ov.abs_diff_over_sigma_anomalous);
out << "_reflns.d_resolution_high " << Fmt(ov.d_min, 2) << "\n";
out << "_reflns.d_resolution_low " << Fmt(ov.d_max, 2) << "\n";
out << "_reflns.number_obs " << ov.unique_reflections << "\n";
@@ -144,6 +147,9 @@ void WriteMmcifReflections(const std::vector<MergedReflection> &reflections,
out << "_reflns.pdbx_netI_over_sigmaI " << Fmt(ov.mean_i_over_sigma, 2) << "\n";
out << "_reflns.pdbx_Rrim_I_all " << Fmt(ov.r_meas, 4) << "\n";
out << "_reflns.pdbx_CC_half " << Fmt(ov.cc_half, 4) << "\n";
if (has_anom)
out << "_reflns.pdbx_absDiff_over_sigma_anomalous " << Fmt(ov.abs_diff_over_sigma_anomalous, 3)
<< " # SigAno = <|dano|>/<sigma(dano)>\n";
out << "_reflns.jfjoch_diffrn_ISa " << CifStr(isa) << " # asymptotic I/sigma (Diederichs)\n";
// Dataset-wide isotropic Wilson B-factor estimate (standard PDBx item), analogous to XDS's
// "WILSON LINE ... B=". Emitted only when the log-linear fit succeeded.
@@ -171,13 +177,18 @@ void WriteMmcifReflections(const std::vector<MergedReflection> &reflections,
out << "_reflns_shell.meanI_over_sigI_obs\n";
out << "_reflns_shell.pdbx_Rrim_I_all\n";
out << "_reflns_shell.pdbx_CC_half\n";
if (has_anom)
out << "_reflns_shell.pdbx_absDiff_over_sigma_anomalous\n";
for (const auto &s : statistics.shells) {
if (s.unique_reflections == 0)
continue;
out << Fmt(s.d_min, 2) << " " << Fmt(s.d_max, 2) << " "
<< s.total_observations << " " << s.unique_reflections << " "
<< Fmt(mult(s), 2) << " " << Fmt(compl_pct(s), 1) << " "
<< Fmt(s.mean_i_over_sigma, 2) << " " << Fmt(s.r_meas, 4) << " " << Fmt(s.cc_half, 4) << "\n";
<< Fmt(s.mean_i_over_sigma, 2) << " " << Fmt(s.r_meas, 4) << " " << Fmt(s.cc_half, 4);
if (has_anom)
out << " " << Fmt(s.abs_diff_over_sigma_anomalous, 3);
out << "\n";
}
out << "#\n";
}