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

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: discuss-gnuradio-bounces+stephan.ludwig2=de.bosch.com@gnu.org [mailto:discuss-gnuradio-bounces+stephan.ludwig2=de.bosch.com@gnu.org] Im Auftrag von Jeff Long
Gesendet: Mittwoch, 19. August 2015 13:31
An: discuss-gnuradio@gnu.org
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
>> Discuss-gnuradio@gnu.org
>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
>


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