Quaternion Discrete Fourier transform
Y = qdft(X, A, L)
qdft(X, A, L) computes the Quaternion Discrete Fourier Transform of the quaternion vector X using transform axis A (direction in 3-space). If X is a matrix, the transforms of the columns are computed.
L specifies the handedness of the transform ('L' or 'R') - determined by the position of the complex exponential relative to X. ('L' gives a transform with the exponential on the left of the signal.)
The transform axis, A must be a pure quaternion (real or complex) but it need not have unit modulus (although the transform itself is computed using a unit-modulus axis, so that the axis is a root of -1).
This function is computed by a rather slow direct evaluation of the QDFT. The related function qfft computes the same result much faster.