# Dealing with \`divide 0\` or \`Inf\` in GNU Radio C++ code **URL:** \ **Category:** GNU Radio\ **Created:** [August 19, 2015, 12:51pm UTC](https://www.ruby-forum.com/t/dealing-with-divide-0-or-inf-in-gnu-radio-c-code/243067 "2015-08-19T12:51:38Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [August 19, 2015, 12:51pm UTC](https://www.ruby-forum.com/t/dealing-with-divide-0-or-inf-in-gnu-radio-c-code/243067/1 "2015-08-19T12:51:38Z")
Let’s think about the following auto/cross correlator: [http://i.imgur.com/Fy5hdVj.png](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](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 [std::numeric\_limits\::infinity - cppreference.com](http://en.cppreference.com/w/cpp/types/numeric_limits/infinity) and [INFINITY - cppreference.com](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. ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 19, 2015, 1:26pm UTC](https://www.ruby-forum.com/t/dealing-with-divide-0-or-inf-in-gnu-radio-c-code/243067/2 "2015-08-19T13:26:41Z")
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 ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 19, 2015, 1:31pm UTC](https://www.ruby-forum.com/t/dealing-with-divide-0-or-inf-in-gnu-radio-c-code/243067/3 "2015-08-19T13:31:22Z")
(That should be “moving averages”, not “correlators”). Also, subtracting instead of dividing might do what you want. Jeff ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 20, 2015, 9:32am UTC](https://www.ruby-forum.com/t/dealing-with-divide-0-or-inf-in-gnu-radio-c-code/243067/4 "2015-08-20T09:32:28Z")
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 Robert Bosch GmbH Corporate Sector Research & Advance Engineering, Communication Technology (CR/AEH4) Renningen 70465 Stuttgart GERMANY > **[Want to know how to live #LikeABosch?](https://www.bosch.com/)** > > Moving stories and inspiring interviews. Experience the meaning of "invented for life" by Bosch completely new. Visit our international website. Tel. +49(711)811-8809 Fax +49(711)811-1052 Mobile +49(172)5630639 [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Registered Office: Stuttgart, Registration Court: Amtsgericht Stuttgart, HRB 14000; Chairman of the Supervisory Board: Franz Fehrenbach; Managing Directors: Dr. Volkmar Denner, Dr. Stefan Asenkerschbaumer, Dr. Rolf Bulander, Dr. Stefan Hartung, Dr. Markus Heyn, Dr. Dirk Hoheisel, Christoph Kbel, Uwe Raschke, Dr. Werner Struth, Peter Tyroller -----Ursprngliche Nachricht----- Von: [discuss-gnuradio-bounces+stephan.ludwig2=removed\_email\_address@domain.invalid](mailto:discuss-gnuradio-bounces+stephan.ludwig2=removed_email_address@domain.invalid) [[mailto:discuss-gnuradio-bounces+stephan.ludwig2=removed\_email\_address@domain.invalid](mailto:discuss-gnuradio-bounces+stephan.ludwig2=removed_email_address@domain.invalid)] Im Auftrag von Jeff L. Gesendet: Mittwoch, 19. August 2015 13:31 An: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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 L. wrote: > > [http://i.imgur.com/Fy5hdVj.png](http://i.imgur.com/Fy5hdVj.png) > > Back to the my correlator, how can I handle such `infinity` value > > In addition, not important. > > > > * * * > > > > Discuss-gnuradio mailing list > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) * * * Discuss-gnuradio mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > **[Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)**