2022 updates to this excellent note:

• with 2.058, zeroes was optimised so that the ndarray is initialised using memset (see https://github.com/PDLPorters/pdl/issues/274 for discussion and measurements).
• with 2.077, the PDL shells have a with_time { code... } function to make this sort of measurement easier.

Observation: the first command of the above snippet is slightly quicker than the rest; this may be because the following ones, in assigning to e.g. $y, will trigger the destruction of the previous contents of that variable, which is likely to take some time.

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