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ENH(fields): allow weights for position fields #173

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Aug 30, 2024
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ENH(fields): allow weights for position fields #173

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17 changes: 10 additions & 7 deletions heracles/fields.py
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Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,7 @@ class Positions(Field, spin=0):

"""

uses = "longitude", "latitude"
uses = "longitude", "latitude", "[weight]"

def __init__(
self,
Expand Down Expand Up @@ -249,23 +249,26 @@ async def __call__(
mapper = self.mapper_or_error

# get catalogue column definition
col = self.columns_or_error
*col, wcol = self.columns_or_error

# position map
pos = mapper.create(spin=self.spin)

# keep track of the total number of galaxies
ngal = 0
wmean, w2mean = 0.0, 0.0

# map catalogue data asynchronously
async for page in aiter_pages(catalog, progress):
if page.size:
lon, lat = page.get(*col)
w = np.ones(page.size)
w = page.get(wcol) if wcol is not None else np.ones(page.size)

mapper.map_values(lon, lat, pos, w)

ngal += page.size
wmean += (w - wmean).sum() / ngal
w2mean += (w**2 - w2mean).sum() / ngal

# clean up to free unneeded memory
del page, lon, lat, w
Expand All @@ -276,8 +279,8 @@ async def __call__(
# effective number of pixels
npix = 4 * np.pi / mapper.area

# compute average number count from map
nbar = ngal / fsky / npix
# compute mean weighted number count per effective mapper "pixel"
nbar = ngal * wmean / fsky / npix
# override with provided value, but check that it makes sense
if (nbar_ := self.nbar) is not None:
# Poisson std dev from expected ngal assuming nbar_ is truth
Expand All @@ -301,8 +304,8 @@ async def __call__(
pos -= vis
del vis

# compute bias of number counts
bias = ngal / (4 * np.pi) * mapper.area**2 / nbar**2
# compute bias of positions, including weight variance
bias = ngal / (4 * np.pi) * mapper.area**2 * (w2mean / nbar**2)

# set metadata of array
update_metadata(pos, catalog, nbar=nbar, bias=bias)
Expand Down
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