# Undefined symbol:fftwf\_execute

**URL:** <https://www.ruby-forum.com/t/undefined-symbol-fftwf-execute/232974>\
**Category:** GNU Radio\
**Created:** [November 8, 2014, 9:01am UTC](https://www.ruby-forum.com/t/undefined-symbol-fftwf-execute/232974 "2014-11-08T09:01:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [November 8, 2014, 9:01am UTC](https://www.ruby-forum.com/t/undefined-symbol-fftwf-execute/232974/1 "2014-11-08T09:01:36Z")

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Dear all,

I am trying to implement cross correlation block using fftw library. I  
follow the correlation example in the gr-lte. when I try to run the  
block I  
get the following error: importError:  
/usr/local/lib/libgnuradio-my\_xcorr.so: undefined symbol: fftwf\_execute  
I have fftw installed.  
Any help?

Regards,  
Saran

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**Author:** ![sarankumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e36b37/32.png) [@sarankumar](https://www.ruby-forum.com/u/sarankumar)\
**Post date:** [November 9, 2014, 10:02pm UTC](https://www.ruby-forum.com/t/undefined-symbol-fftwf-execute/232974/2 "2014-11-09T22:02:01Z")

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Hello Sarankumar,

this very likely points to a linker problem. You have to make sure you  
link against the right fftw libraries in your CMakeLists.txt’s.

Best regards,  
Marcus