Re: Rounding errors?

[Sean Middleditch <elanthis@...>]

Correct me if I'm wrong, but floating point values being an
approximation, this is rather normal.  Computers do not accurately store
floating point values (at least on no architecture I've ever used). 
This is why banking software is written with integer values only.  ~,^

On Wed, 2002-09-18 at 13:17, Ian Latham wrote:
> Hi, I was wondering if someone could enlighten me as to why the
> following script does not produce the output I would expect:
> 
> x=0
> upper_bound = 1
> while x<upper_bound do
> x=x+.01
> print(x)
> end
> 
> I would expect to see all the values in the interval (0,.5] listed out
> at .01 increments to a precision of .01, but instead I get this:
> 
> 0.01
> 0.02
> 0.03
> 0.04
> 0.05
> 0.06000000000000001
> 0.07000000000000001
> 0.08
> 0.09
> 0.09999999999999999
> 0.11
> 0.12
> 0.13
> 0.14
> 0.15
> 0.16
> 0.17
> 0.18
> 0.19
> 0.2
> 0.2100000000000001
> 0.2200000000000001
> 0.2300000000000001
> 0.2400000000000001
> 0.2500000000000001
> 0.2600000000000001
> 0.2700000000000001
> 0.2800000000000001
> 0.2900000000000001
> 0.3000000000000001
> 0.3100000000000001
> 0.3200000000000001
> 0.3300000000000001
> 0.3400000000000001
> 0.3500000000000001
> 0.3600000000000002
> 0.3700000000000002
> 0.3800000000000002
> 0.3900000000000002
> 0.4000000000000002
> 0.4100000000000002
> 0.4200000000000002
> 0.4300000000000002
> 0.4400000000000002
> 0.4500000000000002
> 0.4600000000000002
> 0.4700000000000003
> 0.4800000000000003
> 0.4900000000000003
> 0.5000000000000002
> 
> Can someone explain the extra decimals? Is this a rounding error? An
> error in the internal representation of the float? A bug in the tostring
> function? A bug in the addition code? Try changing upper_bound to 50 and
> the errors get even more severe.
> 
> 
> Thanks,
> 
> Ian Latham
>