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Postings from October 2003
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Moin,
On Tuesday 07 October 2003 20:42, you wrote:
> On Tue, Oct 07, 2003 at 08:12:13PM +0200, Tels <perl_dummy@bloodgate.com>
wrote:
> > Oh, something fishy is going on:
> >
> > print $x->[0] ** (1 / $n->[0]), "\n";
> > $x->[0] = int( $x->[0] ** (1 / $n->[0]) );
> > print $x->[0],"\n";
> >
> > This produces for $x == [ 81 **3 ] and $n == [3] the following output:
> >
> > 81
> > 80
> >
> > Huh?!? This is with Perl v5.8.0...
>
> $ perl -we'printf "%.16g\n", (81**3)**(1/3)'
> 80.99999999999999
But why does
perl -le "print +(81**3)**(1/3)"
print 81 and not 80.99999999999999? perldoc print only says that it will print
"a string or list of strings" but doesn't mention how print creates the
strings. I guess it uses sprintf ("%.0f") or something internally when it
sees a scalar containing a float, but I couldn't find the place where is
documented how print converts floats to a string. (I am not saying that it
isn't in the doc - I just don't know where to look for it. Where is
perlgoogle when you need it...) At least the print surprised me. But it is
not hard to suprise simpletons like me :)
Also interesting to note is:
te@null:~> perl -Mbignum -le 'print +(81 ** 3) ** (1/3)'
80.99999999999999999999999999999999999996
te@null:~> perl -Mbignum=a,50 -le 'print +(81 ** 3) ** (1/3)'
81.000000000000000000000000000000000000000000000002
Bevor I blame Perl's math returning wonky results, I should check my own
code :-)
Thank you again for your time and bearing with me,
Tels
- --
Signed on Tue Oct 7 23:31:35 2003 with key 0x93B84C15.
Visit my photo gallery at http://bloodgate.com/photos/
PGP key on http://bloodgate.com/tels.asc or per email.
"Where shall I put you? Under H, like Hot, Sexy Mama?"
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