[Octave-bug-tracker] [bug #33104] mat2str returns ugly result (different to Matlab)

[Jordi Gutiérrez Hermoso]

Follow-up Comment #8, bug #33104 (project octave):

Patrick Häcker  wrote:
> I cannot follow the example with 0.69. With 15 digits the applied
> patch is exact (result: '0.69'). Do I miss anything?

It's not exact. It only looks exact. With 0.69, the exact value
represented in memory is
0.689999999999999946709294817992486059665679931640625 =
1553741871442821/2^51, which is closer to 0.6899999999999999 than to
0.69, so by always rounding to 15 decimal digits you're losing a
little precision that you could have saved. Always rounding to 15
digits hides a few details that a lot of people don't understand about
hardware floats at the expense of losing a little precision now and
then. This is fine except when that loss of precision adds up as it
can during a long computation.

As long as you don't use the results of mat2str as anything more than
a human convenience and you don't care about loss of precision,
unilaterally rounding or truncating the result to 15 digits can be
acceptable.


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