facing problem regarding fft and ifft use

assignin('base', 'PClean',eval(['PClean_',num2str(ii)]));

PClean=PClean(1:110000,1);

PClean(1,1)=0;%as 1 element is form 0 frequency and 0 sec .so no reading

assignin('base', 'Pdisturbed',eval(['Pdisturbed_',num2str(ii)]));

Pdisturbed=Pdisturbed(1:110000,1);

Pdisturbed(1,1)=0;%as 1 element is form 0 frequency and 0 sec .so no reading

% Fast Fourier Analyse

% Input

[FFT_PClean] = fft(PClean,length(PClean));

%fft on the entire length of your time series clean signal, length(PClean_f)

FFT_PClean((length(PClean)/2)+2)=[];

 %The other half of the fft about the Nyquist frequency (freq/2) is the ...
 %...complex conjugate of the first half and  therefore mirror images the first half.So throw it away with any loss of information.

%Calculate spectra for clean signal, SPClean from the fft above

[SPClean]=2*((FFT_PClean.*conj(FFT_PClean)/length(PClean))/freq);

%freq is the sampling frequency. The spectrum should be scaled by the length of the time series data ,length(PClean_f) and by the sampling frequency freq

% Output is operated same as above

[FFT_Pdisturbed] = fft(Pdisturbed,length(Pdisturbed)); % length(Pdisturbed_f) should be equal to length(PClean_f) to get the correct frequency ratio.

% Both the clean and corrupt data at the same sampling rate and for the same duration.

FFT_Pdisturbed(length(Pdisturbed)/2+2)=[];%Same as the clean signal. Throw out the mirror image

%Calculate spectra for disturbed signal, SPdisturbed

[SPdisturbed]=2*((FFT_Pdisturbed.*conj(FFT_Pdisturbed)/length(Pdisturbed))/freq);

TFunct= SPClean./SPdisturbed;

TFunct(1,1)=0;

%This is the transfer function which can be used to convert the spectrum of corrupt data that is being measured %thereafter in the tunnel using the tubings of similar length and diameter [similar to the one used to establish your transfer function].

df = freq/length(PClean); %frequency resolution

f = 0:df:freq/2; % frequency vector corresponding to the transfer function; freq/2 is called the Nyquist frequency

f=f';

TFunct=TFunct(1:length(f),1);

T(ii,1:length(f))=TFunct_transpose;

close

end

TFunct_final=mean(T);

TFunct_final=transpose(TFunct_final); [SPCleanobtianed]=TFunct_final.*SPdisturbed(1:length(f),1);

P=ifft(SPCleanobtianed);% I do not know how to make ifft of this.I am not getting the results as expected

filename=sprintf('TFunct_final_%d',sn); save(filename,'TFunct_final');

end close all