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Discrete prolate spheroidal (Slepian) sequences

`dps_seq = dpss(seq_length,time_halfbandwidth)[dps_seq,lambda] = dpss(seq_length,time_halfbandwidth)[...] = dpss(seq_length,time_halfbandwidth,num_seq)[...] = dpss(seq_length,time_halfbandwidth,'interp_method')[...] = dpss(...,Ni)[...] = dpss(...,'trace')`

`dps_seq = dpss(seq_length,time_halfbandwidth)` returns
the first `round(2*time_halfbandwidth)` discrete
prolate spheroidal (DPSS), or Slepian sequences of length `seq_length`. `dps_seq` is
a matrix with `seq_length` rows and `round(2*time_halfbandwidth)` columns. `time_halfbandwidth` must
be strictly less than `seq_length/2`.

`[dps_seq,lambda] = dpss(seq_length,time_halfbandwidth)` returns
the frequency-domain energy concentration ratios of the column vectors
in `dps_seq`. The ratios represent the amount of
energy in the passband [*–W*,*W*]
to the total energy from [*–F _{s}*/2,

`[...] = dpss(seq_length,time_halfbandwidth,num_seq)` returns
the first `num_seq` Slepian sequences with time half
bandwidth product `time_halfbandwidth` ordered by
their energy concentration ratios. If `num_seq` is
a two-element vector, the returned Slepian sequences range from `num_seq(1)` to `num_seq(2)`.

`[...] = dpss(seq_length,time_halfbandwidth,'interp_method')` uses
interpolation to compute the DPSSs from a user-created database of
DPSSs. Create the database of DPSSs with `dpsssave` and
ensure that the resulting file, `dpss.mat`, is in
the MATLAB^{®} search path. Valid options for `'interp_method'` are `'spline'` and `'linear'`.
The interpolation method uses the Slepian sequences in the database
with time half bandwidth product `time_halfbandwidth` and
length closest to `seq_length`.

`[...] = dpss(...,Ni)` interpolates from
DPSSs of length `Ni` in the database dpss.mat.

`[...] = dpss(...,'trace')` prints the method
used to compute the DPSSs in the command window. Possible methods
include: direct, spline interpolation, and linear interpolation.

Percival, D. B., and A. T. Walden. *Spectral Analysis
for Physical Applications.* Cambridge, UK: Cambridge University
Press, 1993.

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