disp(' ')
disp(' inverseFFT.m ')
disp(' ver 1.2  January 19, 2012 ')
disp(' by Tom Irvine  Email: tomirvine@aol.com ')
disp(' ')
disp(' This program calculates the inverse of a double-sided complex FFT');
disp(' ')
disp(' The FFT must have 2^N points, where N is an integer. ');
disp(' ')
%
clear CFFT;
clear Y;
clear YR;
clear YI;
clear TT;
clear ccc;
%
disp(' ');
disp(' Select input format: ');
disp('  1=  Two columns: freq(Hz) complex   ');
disp('  2=Three columns: freq(Hz) real imag ');
%
ifor=input(' ');
%
disp(' ')
disp(' Select file input method ');
disp('   1=external ASCII file ');
disp('   2=file preloaded into Matlab ');
file_choice = input('');
%
if(file_choice==1)
    disp(' Enter the input filename ');
    filename = input(' ','s');
    fid = fopen(filename,'r');
    if(ifor==1)
        CFFT = fscanf(fid,'%g %g',[2 inf]);      
    else
        CFFT = fscanf(fid,'%g %g %g',[3 inf]);
    end
    CFFT=CFFT';
else
    CFFT = input(' Enter the matrix name:  ');
end
%
N=length(CFFT(:,1));
%
out3 = sprintf('\n Number of Samples  = %d \n',N);
disp(out3);
%
iflag=0;
%
for(i=1:18)
    if( 2^i == N )
        iflag=1;
        break;
    end
end
%
if( iflag==0)
    disp(' Error: illegal number of samples ');
    disp(' ');
end
%
if(ifor==1)
    ccc=CFFT(:,2);
else
    ccc=complex(CFFT(:,2),CFFT(:,3));
end
%
Y = ifft(ccc,N);  % resume here
%
disp(' Plot the real inverse FFT ')
choice = input(' 1=yes 2=no ');
%
dt=1./max(CFFT(:,1));
%
TT = linspace(0.,N*dt,N);
TT=TT';
%
if(choice == 1)
    figure(1);    
    YR=real(Y);
    plot(TT,YR)
    xlabel(' Time (sec)');
    ylabel(' Amplitude'); 
end
%
disp(' Plot the imaginary inverse FFT ')
choice = input(' 1=yes 2=no ');
%
if(choice == 1)
    figure(1);
    YI=imag(Y);
    plot(TT,YI)
    xlabel(' Time (sec)');
    ylabel(' Amplitude'); 
end