Oops, sorry. It reduced execution time by about 20%. I'm not allowed to post my actual code, but it was just the few obvious changes: declare @mat rather than %mat, and use [] rather than {}.
I made a loop that called levenshtein with 2 arrays of strings of 2-character words. Between one and 25 words per string, comparing all possible combinations of 51 different such "sentences". Hence 51 * 51 = 2061 string comparisons of between one and 25 words per sentence. I executed it on an old MacBook Pro 200 times, and took the average "user" time from the "time" command.
Average "user" time was 19.31% shorter.
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