Re: [Discuss-gnuradio] Dealing with `divide 0` or `Inf` in GNU Radio C++ code.

[Ludwig Stephan (CR/AEH4)]

Hi Jeff,

you could use a strcture like this 
MA_divisor => Divide: %       =>    multiply => pad sink.
           |-> threshold detector    -^

i.e. take the divisor path in parallel into threshold detector and use the 
output (in {0,1}) in a multiplier for masking the dividing by zero cases.

By adjusting the threshold to 0+eps (a small number of your choice), this also 
solves the problem of huge output if the divisor is _almost_ 0.

Best regards

 Stephan Ludwig

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-----Ursprüngliche Nachricht-----
Von: address@hidden [mailto:address@hidden Im Auftrag von Jeff Long
Gesendet: Mittwoch, 19. August 2015 13:31
An: address@hidden
Betreff: Re: [Discuss-gnuradio] Dealing with `divide 0` or `Inf` in GNU Radio 
C++ code.

(That should be "moving averages", not "correlators"). Also, subtracting 
instead of dividing might do what you want.

Jeff

On 08/19/2015 07:25 AM, Jeff Long wrote:
> Jeon,
>
> You can add an appropriate constant before the divide and compensate 
> for it afterward. The exact math will depend on the values coming out 
> of the correlators.
>
> Jeff
>
> On 08/19/2015 06:50 AM, Jeon wrote:
>> Let's think about the following auto/cross correlator:
>> http://i.imgur.com/Fy5hdVj.png
>> I've placed `divide` because I need to normalize the correlation result.
>>
>> If we place `null source`, or `constant source with value of zero` 
>> right before the `pad source`, the simplified form of the correlator 
>> becomes 0 divided by 0.
>>
>> I've placed `time sink` right after the `pad sink` then, I can see 
>> the line hit the infinity. With a simplified flow graph:
>> http://i.imgur.com/Msx9EQj.png
>>
>> Back to the my correlator, how can I handle such `infinity` value 
>> coming into the next block?
>>
>> My guess is that if a source block is a type of float, then 
>> `infinity` might have a maximum value of float. So, I think I can 
>> reject `infinity` value with `if (in[i] > threshold)`, where 
>> `threshold` is big enough, for correlator it is fine to have a value just 
>> larger than one.
>>
>> Do you think what I guess is right? Or can some boost numeric types, 
>> or PMT help somehow to deal with it?
>>
>> In addition, not important.
>> In pages 
>> http://en.cppreference.com/w/cpp/types/numeric_limits/infinity
>> and http://en.cppreference.com/w/cpp/numeric/math/INFINITY,
>> non floating point numeric types can't handle infinity.
>> Is it also applied to GNU Radio?
>>
>> Regards,
>> Jeon.
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
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>>
>


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