[Discuss-gnuradio] a crazy problem with GNURadio fft

[Mostafa Alizadeh]

Hi all, 

I was wonder why my codes in Matlab aren't compatible with GNURadio ones! After all, I found the fft output in GNURadio is different to Matlab!! 

Here is my simple code for fft testing with the real inputs of 0 to 63: 

#include <iostream>

#include <gnuradio/fft/fft.h>

using namespace std;

using namespace gr;

int main()

{

    int fft_size = 64;

    gr::fft::fft_complex *ifft = new gr::fft::fft_complex (fft_size, true, 1);

    // making complex data

    gr_complex in[fft_size];

    for (int i=0; i<fft_size; i++)

    {

        in[i] = i;

    }

    memcpy(ifft->get_inbuf(), in, fft_size);

    ifft->execute();

    cout << "output" << endl;

    for (int i=0; i<fft_size; i++)

    {

        cout << ifft->get_outbuf()[i] << endl;

    }

    cout << "THE END!" << endl;

    return 0;

}

the output in GNURadio:

(28,0)

(24.3326,-13.0209)

(14.591,-22.0217)

(2.07356,-24.4501)

(-9.13707,-20.1094)

(-15.692,-11.1259)

(-16.1531,-1.03318)

(-11.3785,6.63407)

(-4,9.65685)

(2.75122,7.8416)

(6.35844,2.87496)

(5.93264,-2.55936)

(2.38009,-5.98642)

(-2.18793,-6.14396)

(-5.4952,-3.37881)

(-6.11148,0.684235)

(-4,4)

(-0.398263,5.06997)

(2.86434,3.58162)

(4.26461,0.45671)

(3.27677,-2.67271)

(0.553035,-4.28344)

(-2.45947,-3.67857)

(-4.25578,-1.27436)

(-4,1.65685)

(-1.899,3.64105)

(0.940382,3.727)

(3.08336,1.93207)

(3.48022,-0.795649)

(1.9727,-3.06732)

(-0.646391,-3.74757)

(-3.04078,-2.51227)

(-4,0)

(-3.04078,2.51227)

(-0.646391,3.74757)

(1.9727,3.06732)

(3.48022,0.795649)

(3.08336,-1.93207)

(0.940382,-3.727)

(-1.899,-3.64105)

(-4,-1.65685)

(-4.25578,1.27436)

(-2.45947,3.67857)

(0.553035,4.28344)

(3.27677,2.67271)

(4.26461,-0.45671)

(2.86434,-3.58162)

(-0.398263,-5.06997)

(-4,-4)

(-6.11148,-0.684235)

(-5.4952,3.37881)

(-2.18793,6.14396)

(2.38009,5.98642)

(5.93264,2.55936)

(6.35844,-2.87496)

(2.75122,-7.8416)

(-4,-9.65685)

(-11.3785,-6.63407)

(-16.1531,1.03318)

(-15.692,11.1259)

(-9.13707,20.1094)

(2.07356,24.4501)

(14.591,22.0217)

(24.3326,13.0209)

the output of the Matlab:

   1.0e+03 *

   2.0160          

  -0.0320 + 0.6514i

  -0.0320 + 0.3249i

  -0.0320 + 0.2157i

  -0.0320 + 0.1609i

  -0.0320 + 0.1278i

  -0.0320 + 0.1055i

  -0.0320 + 0.0894i

  -0.0320 + 0.0773i

  -0.0320 + 0.0677i

  -0.0320 + 0.0599i

  -0.0320 + 0.0534i

  -0.0320 + 0.0479i

  -0.0320 + 0.0431i

  -0.0320 + 0.0390i

  -0.0320 + 0.0353i

  -0.0320 + 0.0320i

  -0.0320 + 0.0290i

  -0.0320 + 0.0263i

  -0.0320 + 0.0237i

  -0.0320 + 0.0214i

  -0.0320 + 0.0192i

  -0.0320 + 0.0171i

  -0.0320 + 0.0151i

  -0.0320 + 0.0133i

  -0.0320 + 0.0114i

  -0.0320 + 0.0097i

  -0.0320 + 0.0080i

  -0.0320 + 0.0064i

  -0.0320 + 0.0047i

  -0.0320 + 0.0032i

  -0.0320 + 0.0016i

  -0.0320          

  -0.0320 - 0.0016i

  -0.0320 - 0.0032i

  -0.0320 - 0.0047i

  -0.0320 - 0.0064i

  -0.0320 - 0.0080i

  -0.0320 - 0.0097i

  -0.0320 - 0.0114i

  -0.0320 - 0.0133i

  -0.0320 - 0.0151i

  -0.0320 - 0.0171i

  -0.0320 - 0.0192i

  -0.0320 - 0.0214i

  -0.0320 - 0.0237i

  -0.0320 - 0.0263i

  -0.0320 - 0.0290i

  -0.0320 - 0.0320i

  -0.0320 - 0.0353i

  -0.0320 - 0.0390i

  -0.0320 - 0.0431i

  -0.0320 - 0.0479i

  -0.0320 - 0.0534i

  -0.0320 - 0.0599i

  -0.0320 - 0.0677i

  -0.0320 - 0.0773i

  -0.0320 - 0.0894i

  -0.0320 - 0.1055i

  -0.0320 - 0.1278i

  -0.0320 - 0.1609i

  -0.0320 - 0.2157i

  -0.0320 - 0.3249i

  -0.0320 - 0.6514i

Please help me!! I'm totally confused. 

Best