CarpetX’s TSV output, excluding the norms/ files, does not append to a single file per group in the way Carpet’s ASCII output does. Instead, it creates one file per group per iteration: <group>.it000000.<x/y/z>.tsv for grid functions and arrays, and <group>.it000000.tsv for scalars.

Appending subsequent iterations to the same file would make analysis and post-processing easier, while also reducing the amount of output files.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2936/carpetx-tsv-output-does-not-append-files