# Using fftw in c for harmonic analysis

So I have a periodic series and I need to get the highest number of that series without the first harmonic. The series is of size 360 So I have f(0)=value1 f(1)=value2 ... f(359)=value360 Someone suggested that to do this I must get the 360-point discrete fourier transform DFT (f(0), f(1)... f(359)) --> (F(0), F(1)... F(359)) then set F(0) and F(359) to 0 which will remove the first harmonic. After this I should do the 360-point inverse discrete fourier transform iDFT and then search for the highest value among the result. To do this I'm using the fft libraries in c but I'm having some trouble trying to figure it out how to use them properly to do this. My periodic series is made up of real numbers not complex so I do this: #include "complex.h" #include "fftw.h" #include "rfftw.h" ... fftw_real in_r; //input 1d array of real numbers fftw_complex out_c; //output 1d array of complex numbers rfftwnd_plan p_DFT; //plan to calculate the DFT rfftwnd_plan p_iDFT; //plan to calculate the iDFT p_DFT = rfftwnd_create_plan(1, 360, FFTW_REAL_TO_COMPLEX, FFTW_MEASURE); p_iDFT = rfftwnd_create_plan(1, 360, FFTW_COMPLEX_TO_REAL, FFTW_MEASURE); rffftwnd_one_real_to_complex(p_DFT,in_r,out_c); //I GET AN ERROR IN BOTH THIS CALLS: incompatible types when assigning to type //â€˜fftw_complexâ€™ from type â€˜complex doubleâ€™ out_c=0.0 + 0.0*_Complex_I; out_c=0.0 + 0.0*_Complex_I; rfftwnd_one_complex_to_real(p_iDFT,out_c,in_r); for(i=0;i<360;i++) max=fmaxf(in_r[i],max); So I have several questions. First how can I set the first and last element of the output array to 0 considering it is complex but doesn't let me asign a complex number to it? Second, is how I'm doing this correct? or am I missing something? Third (this is a follow up of what I need to do next). Can I use the FFTW libraries to get the amplitude and phase of the first to fourth harmonics of the series? If so, how? Thanks for any help. UPDATE: I changed #include "fftw.h" for #include "fftw3.h" So on my includes I have #include "complex.h" #include "fftw3.h" #include "rfftw.h" But I'm getting the same error UPDATE 2: I'm also getting errors like this /usr/include/fftw.h:307:13: error: conflicting types for â€˜fftw_destroy_planâ€™ Because of including rfftw.h after fftw3.h. But if I delete rfftw.h then I get errors like this error: unknown type name â€˜fftw_realâ€™ There seems to be a conflict between fftw3.h and rfftw.h but I can't delete rfftw.h because then I can't use the functions I need.
Which compiler do you use?

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