Please check that arr_coarse is created in spectral space with the right shape (cf. https://fluidfft.readthedocs.io/en/latest/ipynb/executed/tuto_fft3d_mpi_domain_decomp.html#summary)
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Please check that arr_coarse is created in spectral space with the right shape (cf. https://fluidfft.readthedocs.io/en/latest/ipynb/executed/tuto_fft3d_mpi_domain_decomp.html#summary)