analysis: reject calc_rh for chains shorter than 2 beads - #5371
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jngrad merged 3 commits intoJul 15, 2026
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The hydrodynamic radius is computed as a sum over distinct bead pairs with a 0.5*N*(N-1) prefactor. For a single-bead chain (chain_length==1) there are no pairs: the prefactor is 0 and the accumulated inverse distance ri stays 0, so calc_rh evaluated prefac/ri = 0.0/0.0 = NaN and returned a silent NaN array instead of reporting the ill-posed request. check_topology only rejects chain_length<=0 and is shared with calc_re and calc_rg, where single-bead chains are valid (R_e==0, R_g==0), so the guard cannot live there. Add a calc_rh-specific precondition in the script-interface dispatch that throws std::domain_error (surfaced as a Python ValueError, consistent with the other chain-analysis domain checks) when chain_length < 2. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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…5371) Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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…5371) Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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The hydrodynamic radius is computed as a sum over distinct bead pairs
with a 0.5N(N-1) prefactor. For a single-bead chain (chain_length==1)
there are no pairs: the prefactor is 0 and the accumulated inverse
distance ri stays 0, so calc_rh evaluated prefac/ri = 0.0/0.0 = NaN and
returned a silent NaN array instead of reporting the ill-posed request.
check_topology only rejects chain_length<=0 and is shared with calc_re
and calc_rg, where single-bead chains are valid (R_e==0, R_g==0), so the
guard cannot live there. Add a calc_rh-specific precondition in the
script-interface dispatch that throws std::domain_error (surfaced as a
Python ValueError, consistent with the other chain-analysis domain
checks) when chain_length < 2.
Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com
🤖 Generated with Claude Code