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Bugfix: jvp now supports alternate mode ordering #160

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Bugfix: jvp now supports alternate mode ordering #160

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950bc35
fix for different mode orderings in jvp
TomHilder Aug 20, 2025
a7bf794
undo changes to inputs from my formatter
TomHilder Aug 20, 2025
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21 changes: 20 additions & 1 deletion src/jax_finufft/ops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,22 @@ def nufft2(source, *points, iflag=-1, eps=1e-6, opts=None):
return index.unflatten(result)


def get_frequency_array(n, modeord):
if modeord == 0:
return np.arange(-np.floor(n / 2), np.floor((n - 1) / 2 + 1))
elif modeord == 1:
if n % 2 == 0:
pos = np.arange(0, n // 2)
neg = np.arange(-n // 2, 0)
return np.concatenate([pos, neg])
else:
pos = np.arange(0, (n + 1) // 2)
neg = np.arange(-(n - 1) // 2, 0)
return np.concatenate([pos, neg])
else:
raise ValueError(f"Unsupported modeord: {modeord}")


def jvp(prim, args, tangents, *, output_shape, iflag, eps, opts):
# Type 1:
# f_k = sum_j c_j * exp(iflag * i * k * x_j)
Expand All @@ -75,6 +91,9 @@ def jvp(prim, args, tangents, *, output_shape, iflag, eps, opts):
source, *points, output_shape=output_shape, iflag=iflag, eps=eps, opts=opts
)

# Extract modeord from opts
modeord = opts.modeord if hasattr(opts, "modeord") else 0

# The JVP op can be written as a single transform of the same type with
output_tangents = []
ndim = len(points)
Expand Down Expand Up @@ -105,7 +124,7 @@ def jvp(prim, args, tangents, *, output_shape, iflag, eps, opts):
n = source.shape[-ndim + dim] if output_shape is None else output_shape[dim]
shape = np.ones(ndim, dtype=int)
shape[dim] = -1
k = np.arange(-np.floor(n / 2), np.floor((n - 1) / 2 + 1))
k = get_frequency_array(n, modeord)
k = k.reshape(shape)
factor = 1j * iflag * k
dx = dx[:, None, :]
Expand Down
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