[Oberon] real math

[rob solomon]

That printf format code is rounding your r.

I was always taught to compare real numbers this way:
   ABS(r-480.0) < 1.e-6

Or whatever tolerance value works for you.  I was taught that comparing 
real numbers for = or not= will not do what you want.



On 11/13/2014 06:47 AM, oberon at moravcik.info wrote:
> Hi Jörg,
>
> just tested your code below and it outputs again 480....32 as in my other email I sent today.
>
> Basically I need to test that 480/100*100 is 480 without some decimal digits at the end
> because I am comparing two computed real numbers if they are less, greater or equal.
> Comparing 480.0 with 480.0...32 does not make those two equal.
>
> I rounded the computed real numbers to 2 decimal digits which is enough precision in my case.
> This way the problem was solved but I do not think this is the general solution.
> Note that linux gcc compiler returns 480
>   printf("result: %3.15f", 480.0/100.0*100.0);
>
>
> Zdenek
>
>
>
> On Mon, Nov 10, 2014 at 06:50:02PM +0100, Jörg wrote:
>> Hi Zdenek
>>
>> I just compiled your code with AOS on Windows.
>>
>> - - - -
>> MODULE RealTest;
>> IMPORT Commands;
>>
>> PROCEDURE Do*(ctx: Commands.Context);
>>    VAR
>>      r: REAL;
>>    BEGIN
>>      r := 480 / 100 * 100;
>>      ctx.out.Int( ENTIER(r*1000000), 0);
>>    END Do;
>>
>> BEGIN
>> END RealTest.Do ~
>> - - - - -
>>
>> On my PC the output is 480000000. So, I don't have the same effect as you
>> have.
>>
>> Generally, checking REALs on equality is a little dangerous. You should
>> rather subtract two REALs and check for an epsilon>0.
>>
>> I wonder what the use case of your code is? What do you want to find out by
>> dividing 480 by 100 and multiplying it by 100 again. Do you want to round a
>> number to two digits?
>>
>> br
>> Jörg
>>
>> -----Original Message-----
>> From: oberon at moravcik.info [mailto:oberon at moravcik.info]
>> Sent: Sonntag, 9. November 2014 20:36
>> To: oberon at lists.inf.ethz.ch
>> Subject: [Oberon] real math
>>
>> Hi,
>>
>> following code returns imprecise real number:
>>
>>   r : REAL;
>>
>>   r := 480 / 100 * 100;
>>   out.Int( ENTIER(r * 1000000) , 0 );
>>
>> outputs 48000019 instead of 48000000
>>
>> How to check that 480/100*100 is 480 again ?
>>
>> Thanks
>> Zdenek
>>
>> --
>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
>> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>
>
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>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
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