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maplog: change quantization to match updated data model #210

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9 changes: 5 additions & 4 deletions abacusnbody/data/maplog.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,8 @@
reference unpacker's pattern for ``mult_sec`` and ``pid``) so columns are
safe to read without filtering. Use ``node_type`` as the discriminator.

Position is returned in Mpc/h (5 kpc/h quantum, fixed); velocity in km/s
(via the vect32 encoding shared with ``output_particle``).
Position is returned in Mpc/h (1/128 Mpc/h ≈ 7.8 kpc/h quantum, fixed);
velocity in km/s (via the vect32 encoding shared with ``output_particle``).

The C++ source-of-truth is ``maplog.cc`` / ``vect32.cc`` in the Abacus
codebase. The reference Python unpacker is
Expand Down Expand Up @@ -44,9 +44,10 @@
NODE_TIMESLICE = 3
NODE_CONTROL_MASK = 0x3

# Position encoding: 21 bits per axis, centered at 2^20, 5 kpc/h quantum.
# Position encoding: 21 bits per axis, centered at 2^20, 1/128 Mpc/h
# (~7.8 kpc/h) quantum. Range is ±8192 Mpc/h.
_POS_OFFSET = 1 << 20 # 1048576
_POS_SCALE = 200.0 # quanta per Mpc/h (1 / 0.005)
_POS_SCALE = 128.0 # quanta per Mpc/h
_POS_MASK = (1 << 21) - 1 # 0x1FFFFF


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