scripts/iomega.m

function dataout =  iomega(datain, dt, datain_type, dataout_type)
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%
%   IOMEGA is a MATLAB script for converting displacement, velocity, or
%   acceleration time-series to either displacement, velocity, or
%   acceleration times-series. The script takes an array of waveform data
%   (datain), transforms into the frequency-domain in order to more easily
%   convert into desired output form, and then converts back into the time
%   domain resulting in output (dataout) that is converted into the desired
%   form.
%
%   Variables:
%   ----------
%   
%   datain       =   input waveform data of type datain_type
%
%   dataout      =   output waveform data of type dataout_type
%
%   dt           =   time increment (units of seconds per sample)
%
%                    1 - Displacement
%   datain_type  =   2 - Velocity
%                    3 - Acceleration
%
%                    1 - Displacement
%   dataout_type =   2 - Velocity
%                    3 - Acceleration
%
%
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    %   Make sure that datain_type and dataout_type are either 1, 2 or 3
    if (datain_type < 1 || datain_type > 3)
        error('Value for datain_type must be a 1, 2 or 3');
    elseif (dataout_type < 1 || dataout_type > 3)
        error('Value for dataout_type must be a 1, 2 or 3');
    end
    %   Determine Number of points (next power of 2), frequency increment
    %   and Nyquist frequency
    N = 2^nextpow2(max(size(datain)));
    df = 1/(N*dt);
    Nyq = 1/(2*dt);
    %   Save frequency array
    iomega_array = 1i*2*pi*(-Nyq : df : Nyq-df);
    iomega_exp = dataout_type - datain_type;
    %   Pad datain array with zeros (if needed)
    size1 = size(datain,1);
    size2 = size(datain,2);
    if (N-size1 ~= 0 && N-size2 ~= 0)
        if size1 > size2
            datain = vertcat(datain,zeros(N-size1,1));
        else
            datain = horzcat(datain,zeros(1,N-size2));
        end
    end
    %   Transform datain into frequency domain via FFT and shift output (A)
    %   so that zero-frequency amplitude is in the middle of the array 
    %   (instead of the beginning)
    A = fft(datain);
    A = fftshift(A);
    %   Convert datain of type datain_type to type dataout_type
    for j = 1 : N
        if iomega_array(j) ~= 0
            A(j) = A(j) * (iomega_array(j) ^ iomega_exp);
        else
            A(j) = complex(0.0,0.0);
        end
    end
    %   Shift new frequency-amplitude array back to MATLAB format and
    %   transform back into the time domain via the inverse FFT.
    A = ifftshift(A);
    datain = ifft(A);    
    %   Remove zeros that were added to datain in order to pad to next
    %   biggerst power of 2 and return dataout.
    if size1 > size2
        dataout = real(datain(1:size1,size2));
    else
        dataout = real(datain(size1,1:size2));
    end
    return