Why do quotes in norm for infinity norm sometimes work

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Michael Gustafson
Michael Gustafson 2013-12-9
评论： dpb 2013-12-9
I'm just curious as to why, for some matrix A, you can calculate the infinity norm with
  • norm(A, inf)
  • norm(A, Inf)
  • norm(A, 'inf')but not
  • norm(A, 'Inf')
especially when
>> inf
ans =
Inf
Seems strange to have included 'inf' -- and the command itself doesn't indicate that 'inf' is a valid input either:
>> norm(A, 'Inf')
Error using norm
The only matrix norms available are 1, 2, inf, and 'fro'.

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dpb
dpb 2013-12-9
"Because" :)
It appears the author of norm did go as far as to do a string comparison of the inputs but didn't bother to [upper/lower]case the input string before making the comparison internally.
The same case-sensitive comparison fails in the same fashion with 'Fro' as opposed to 'fro'
  2 个评论
Michael Gustafson
Michael Gustafson 2013-12-9
I thought it might be that :) I seem to remember at some point in the past, 'inf' wasn't accepted either... At least, that's how I graded things, but a student this semester pointed out that the lower case version in quotes did work (and now I don't have any old enough MATLAB installations to check The Good Old Days)
dpb
dpb 2013-12-9
It works same way as far back as R12; I don't have anything earlier installed.

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