BigInt bug?

shao.lo has asked for the wisdom of the Perl Monks concerning the following question:

use Math::BigInt;
my $n = 2;
my $k = 0;
my $x = Math::BigInt->new($n);
my $z = $x->bnok($k);
printf("$n choose $k = %d\n", $z);
printf("$n choose $k = %d\n", $z->as_int());
printf("$n choose $k = %s\n", $z->bstr());
printf("$n choose $k = %d\n", $z->numify());
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I'm guessing I'm doing something wrong because this just prints 2 choose 0 = 3. I'm pretty sure it should be 1.

my $n = 5;
my $k = 2;
my $x = Math::BigInt->new($n);
my $z = $x->bnok($k);
printf("$n choose $k = %d\n", $z);
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The above correctly prints 5 choose 2 = 10. So, what am I doing wrong? Or is bnok() broken?? BTW..I tried BigFloat too...with same result.

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THANKS to everyone that responded. I was indeed using an older verion (1.89_01). I use Ubuntu and I guess Math::BigInt comes as part of some other package. When I installed it directly via 'apt-get install libmath-bigint-perl' I now get version (1.993) which does indeed get the 2 choose 0 correct.

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Thanks again for the responses!

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Replies are listed 'Best First'.
Re: BigInt bug? by davido (Cardinal) on Mar 07, 2012 at 07:05 UTC
If you're using a version of Math::BigInt older than version 1.90, you may want to upgrade to the latest. I found this entry in the CHANGES log for the Math::BigInt distribution: `2010-09-03 v1.90 rafl * fix bnok() for k==0 and k==n-1` [download] It looks like the bug-fix in version 1.90 targeted the bug you're experiencing. Dave	[reply] [d/l]
Re: BigInt bug? by tobyink (Canon) on Mar 07, 2012 at 06:46 UTC
The output of your first script is correct on this machine: 2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1 Perl 5.10.1, Math::BigInt 1.95.	[reply]
Re^2: BigInt bug? by bitingduck (Deacon) on Mar 07, 2012 at 07:08 UTC
using 5.10.1, Math::BigInt 1.89 I get `2 choose 0 = 3 2 choose 0 = 3 2 choose 0 = 3 2 choose 0 = 3` [download] I then updated to Math::BigInt 1.997 and I get `2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1` [download] Looks like you found a bug that's been fixed. (and helped me update...)	[reply] [d/l] [select]
Re^3: BigInt bug? by lutok (Scribe) on Mar 07, 2012 at 11:06 UTC
Using 5.14.2, Math::BigInt 1.994 I get `2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1 2 choose 0 = 1` [download]	[reply] [d/l]