From: teeshift <teeshift@...>
Date: 2006-12-01T10:05:09+09:00
Subject: floating point problem... floating indeed :(

I recently wrote a code and haven't been found the bug and start
suspecting that it was
the floating computation that causing the problem. I did a little
experiement and found the
following phenomena:

I am using

Linux source 2.6.15-27-386 #1 PREEMPT Sat Sep 16 01:51:59 UTC 2006 i686
GNU/Linux
Ubuntu is the OS.

#####################
#!/usr/bin/ruby1.9

a = 1.0

a.to_f

while(a < 15.0)
  a = a + 0.1
  print a,"\t",a * a,"\n"
end
#####################

and the output is...(as following) quite odd.  Anyone can explain it?
or a way to avoid it (while
keeping the precision)


1.1     1.21
1.2     1.44
1.3     1.69
1.4     1.96
1.5     2.25
1.6     2.56
1.7     2.89
1.8     3.24
1.9     3.61
2.0     4.0
2.1     4.41
2.2     4.84
2.3     5.29000000000001
2.4     5.76000000000001
2.5     6.25000000000001
2.6     6.76000000000001
2.7     7.29000000000001
2.8     7.84000000000001
2.9     8.41000000000001
3.0     9.00000000000001
3.1     9.61000000000001
3.2     10.24
3.3     10.89
3.4     11.56
3.5     12.25
3.6     12.96
3.7     13.69
3.8     14.44
3.9     15.21
4.0     16.0
4.1     16.81
4.2     17.64
4.3     18.49
4.4     19.36
4.5     20.25
4.6     21.16
4.7     22.09
4.8     23.04
4.9     24.01
5.0     25.0
5.1     26.01
5.2     27.04
5.3     28.09
5.4     29.16
5.5     30.25
5.6     31.36
5.7     32.49
5.8     33.64
5.9     34.81
6.0     35.9999999999999
6.1     37.2099999999999
6.19999999999999        38.4399999999999
6.29999999999999        39.6899999999999
6.39999999999999        40.9599999999999
6.49999999999999        42.2499999999999
6.59999999999999        43.5599999999999