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function res = fft1 (D, N, DIM)
// Description
// Calculates the discrete Fourier transform of a matrix using Fast Fourier Transform algorithm.
// The FFT is calculated along the first non-singleton dimension of the array. Thus, FFT is computed for each column of D.
// The variable 'N' is an integer that determines the number of elements of 'D' to use.
// If 'N' is larger than the dimension along which the FFT is calculated,
// then 'D' is resized and padded with zeros to match the required size.On the other hand,
// if 'N' is smaller than the size of 'D', then 'D' is truncated to match the required size.
// DIM is an integer specifying the dimension of the matrix along which the FFT is performed.
// Calling Sequence
// fft1 (D)
// fft1 (D, N)
// fft1 (D, N, DIM)
// Parameters
// D: input matrix
// N: Specifies the number of elements of x to be used
// DIM: Specifies the dimention of the matrix along which the FFT is performed
// Examples
// D = [1 2 3; 4 5 6; 7 8 9]
// N = 3
// DIM = 2
// fft1 (D,N,DIM)
// ans =
// 6.0000 + 0.0000i -1.5000 + 0.8660i -1.5000 - 0.8660i
// 15.0000 + 0.0000i -1.5000 + 0.8660i -1.5000 - 0.8660i
// 24.0000 + 0.0000i -1.5000 + 0.8660i -1.5000 - 0.8660i
funcprot(0);
lhs = argn(1)
rhs = argn(2)
if (rhs < 1 | rhs > 3)
error("Wrong number of input arguments.")
end
dimension = size(D);
// first non-singleton dimension
nsdim = find(dimension >1,1)
if isempty(nsdim) then
nsdim = 1 // default to 1 to avoid error while calling fft
end
select(rhs)
case 1 then
res = fft(D, -1, nsdim);
case 2 then
if isempty(N) then
n = size(D, nsdim);
else
n = N;
end
new_size = size(D);
new_size(nsdim) = n;
D = resize_matrix(D, new_size);
res = fft(D, -1, nsdim);
case 3 then
if isempty(N) then
n = size(D, DIM);
else
n = N;
end
new_size = size(D);
new_size(DIM) = n;
D = resize_matrix(D, new_size);
res= fft(D, -1, DIM);
end
endfunction
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