DOUBLEN is the jSpectral module of jLab.

  DOUBLEN  Interpolates a time series to double its length.
    Y=DOUBLEN(X) for a column vector X of length M, returns the
    interpolation of X to length 2M.  M must be even.
    For matrix X of size M x N, each column is interpolated to length
    2M, and Y is size 2M x N.
    The interpolated vector Y may be considered to be of the same
    duration, but with twice the sample rate, as the original vector.
    In the interpolated vector, all frequencies higher than the
    original Nyquist are set to zero.
    DOUBLEN uses the frequency-domain zero padding algorithm of Mallat
    (1999), second edition, Section 4.5.4.
    'doublen --t' runs a test.
    'doublen --f' generates a sample figure.
    This is part of JLAB --- type 'help jlab' for more information
    (C) 2004--2015  J.M. Lilly --- type 'help jlab_license' for details        

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