[Jprogramming] dyad ": rounding error

[bill lam]

I agree that technically 0.295 could be rounded to 0.29, but I think that most 
people (programmer or non-programmer) will expect that rounding the quotient 
(295/1000) to 2 decimal places is 0.30

I also double checked with a pocket calculator.

Joey K Tuttle wrote:
> It would be a shame to slow down ": ... consider
> 
>    0j20 ": 0.295 0.2995
> 0.29499999999999998446 0.29949999999999998845
> 
> I suppose that 8!:x implements the "standard rule" that
> rounding a number ending (but not really in this case) 5
> depends on whether the prior digit is odd or even. Much
> of this seems arbitrary at best.
> 
> - joey
> 
> 
> At 8:45 AM -0700 3/19/07, Roger Hui wrote:
>> The difference is that the dyad ": depends on the
>> C library routines whereas 8!:x do the programming
>> themselves and take more care.  I'll look into it.
>> It is likely that a fix will make ": slower.
>>
>> Thanks for the report.
>>
>>
>>
>> ----- Original Message -----
>> From: bill lam <bbill.lam at gmail.com>
>> Date: Sunday, March 18, 2007 11:14 pm
>> Subject: [Jprogramming] dyad ": rounding error
>>
>>>  On both J504 and J601, dyad ": sometimes does not round properly
>>>  on some
>>>  numbers, eg.
>>>     0j2 ":  0.295
>>>  0.29
>>>     0j3 ":  0.2995
>>>  0.299
>>>
>>>  incidentally 8!:x family of J601 does not have this problem,
>>>     '0.2' (8!:0) 0.295
>>>  +----+
>>>  |0.30|
>>>  +----+
>>>     '0.2' (8!:1) 0.295
>>>  +----+
>>>  |0.30|
>>>  +----+
>>>     '0.2' (8!:2) 0.295
>>>  0.30
>>>     '0.3' (8!:2) 0.2995
>>>  0.300
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-- 
regards,
bill