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use scatter add in test of drawing full scenes #266

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Merged
beckermr merged 2 commits into from
Sep 18, 2026
Merged

use scatter add in test of drawing full scenes #266

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95dee34
use scatter add in test of drawing full scnes for future reference
ismael-mendoza Sep 18, 2026
764e5f2
jit like the old one just in case
ismael-mendoza Sep 18, 2026
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26 changes: 12 additions & 14 deletions tests/jax/test_render_scene.py
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Original file line number Diff line number Diff line change
Expand Up @@ -183,14 +183,17 @@ def _draw_stamp_jgs(
return stamp


@partial(jax.jit, static_argnames=("slen",))
def _add_to_image(carry, x, slen):
image = carry[0]
stamp = x

image[stamp.bounds] += stamp

return (image,), None
@jax.jit
def _scatter_stamps_into_image(image: jgs.ImageD, stamps: jgs.ImageD) -> jgs.ImageD:
"""Add a batch of same-size ``stamps`` into ``image`` with a single vectorized scatter-add."""
n, slen, _ = stamps.array.shape
row0 = stamps.bounds.ymin - image.bounds.ymin
col0 = stamps.bounds.xmin - image.bounds.xmin
local = jnp.arange(slen)
rows = jnp.broadcast_to(row0[:, None, None] + local[None, :, None], (n, slen, slen))
cols = jnp.broadcast_to(col0[:, None, None] + local[None, None, :], (n, slen, slen))
new_array = image.array.at[rows, cols].add(stamps.array)
return jgs.ImageD(new_array, wcs=image.wcs, bounds=image.bounds)


@partial(jax.jit, static_argnames=("fft_size", "slen", "ilen", "ng"))
Expand All @@ -217,12 +220,7 @@ def _render_scene_stamps_jax_galsim(
jnp.pad(image.array, slen), wcs=image.wcs, bounds=image.bounds.withBorder(slen)
)

final_pad_image = jax.lax.scan(
partial(_add_to_image, slen=slen),
(pad_image,),
xs=stamps,
length=ng,
)[0][0]
final_pad_image = _scatter_stamps_into_image(pad_image, stamps)

return stamps, final_pad_image

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