Finufft tests fail

[janden]

In particular, testTransform1_32, testTransform1_64, testTransformMany1_32, and testTransformMany1_64 in test_nufft fail. This started with the upgrade to Finufft 2.0.4.

From a first look, it seems that this is not small discrepancy. For example, my local output for testTransform1_32 gives all NaNs. Will continue to investigate.

[janden]

So the following example reproduces the bug:

import numpy as np

from finufft import Plan

np.random.seed(0)

shape = (8, 8, 8)
n_pts = 4
dtype = 'float32'
dtype_complex = 'complex64'

x = np.random.randn(*shape).astype(dtype)
pts = 2 * np.pi * (np.random.rand(len(shape), n_pts).astype(dtype) - 0.5)

eps = np.finfo(dtype).eps

plan = Plan(nufft_type=2, n_modes_or_dim=shape, eps=eps, n_trans=1,
        dtype=dtype)

plan.setpts(*pts)

result = plan.execute(x)

grid = np.mgrid[-shape[0] // 2:shape[0] // 2, -shape[1] // 2:shape[1] // 2,
        -shape[2] // 2:shape[2] // 2]

result_ref = np.empty(n_pts, dtype=dtype_complex)

for k in range(n_pts):
    result_ref[k] = np.sum(x * np.exp(-1j * (grid[0] * pts[0, k] + grid[1] *
        pts[1, k] + grid[2] * pts[2, k])))

err = np.max(np.abs(result - result_ref))


print(f"{err=}")

Error is about 5e-5 for 2.0.3 but 2e28 (or nan) for 2.0.4.

[janden]

Will forward this onto Finufft. Will put in a PR to restrict versions to <2.0.4 for now.