I'm a Perl novice and hope this is a proper channel for a simple 
question.  Why does the following decrement incorrectly below 10?  It 
works with $i -- or $i -= .5.  This is part of a larger script and I've 
made a workaround, but I'm still curious.

use Math::Complex;

for ($i = 13; $i >= 1; $i -= .1) {
 print"$i\n";
}

11
10.9
10.8
10.7
10.6
10.5
10.4
10.3
10.2
10.1
10
9.90000000000001
9.80000000000001
9.70000000000001
9.60000000000001
9.50000000000001
9.40000000000001
9.30000000000001
9.20000000000001
9.10000000000001
9.00000000000001