Re^2: Is this odd behavior a floating point problem?

in reply to Re: Is this odd behavior a floating point problem?
in thread Is this odd behavior a floating point problem?

:D Looks like two separate off-by-one error (OBOE) errors to me :)

First you start with non-zero and add 40 times (one too many), then you start with non-zero and add 41 times (one too many twice).

If you start with non-zero you need to add only 39 times, or start with zero and add 40 times :)

In short

perl -MData::Dump -e " @f = map { 0.001 } 1 .. 40; dd\@f; $o = 0; for(
+@f){ dd $o+=$_; } dd int @f; dd $o/int(@f); "

perl -MData::Dump -e "  $o = 0; for(1 .. 40){ dd $o+= 0.001; } dd $o/4
+0; "
[download]

It didn't dawn on me to check wickedjesters (or your) math until ww raised the quesiton

Comment on Re^2: Is this odd behavior a floating point problem? Download Code

Replies are listed 'Best First'.
Re^3: Is this odd behavior a floating point problem? by Eliya (Vicar) on Mar 24, 2012 at 01:09 UTC
... you start with non-zero ... Not sure what you're talking about. n times adding x to zero is mathematically (but not necessarily numerically) the same as n * x. `$ perl -le '$sum += 1 for 1..40; print $sum' 40` [download] So where is the problem? I think you overlooked that `$sum` is initially undef/zero.	[reply] [d/l] [select]

In Section Seekers of Perl Wisdom