| Subject: | batan2(1,0) not following global accuracy() |
| Date: | Wed, 01 May 2013 06:50:23 +1000 |
| To: | bug-Math-BigInt [...] rt.cpan.org |
| From: | Kevin Ryde <user42 [...] zip.com.au> |
In Math::BigFloat 1.997 and recent debian i386 perl 5.14.3, if a global
Math::BigFloat->accuracy(100) has been set then batan2() of Y=1,X=0 only
gives 40 decimal places of accuracy, not the requested 100. Eg. the
program atan2.pl below prints
1.570796326794896619231321691639751442098000000000000000000000000000000000000000000000000000000000000
whereas I expected the trailing 0s to be some non-zero value.
If $x is some small non-zero value, such as 1e-10 then the desired full
100 decimals are returned.
In the code I wonder if the special cases for X=0 and Y=0 giving pi/2
etc could look also at the accuracy() and/or precision setting on $y or
$x or global or whatever, so as to ensure the result in those cases is
the same accuracy as the general case.
use strict;
use Math::BigFloat;
Math::BigFloat->accuracy(100);
my $y = Math::BigFloat->new(1);
my $x = Math::BigFloat->new(0);
$y->batan2($x);
print "$y\n";