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dpssdir

Manage discrete prolate spheroidal sequences database directory

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Syntax

dpssdir
dpssdir(seqLength)
dpssdir(timeHalfBW,"NW")
dpssdir(seqLength,timeHalfBW)
index = dpssdir(___)

Description

dpssdir lists the directory of saved sequences in dpss.mat. Create the DPSS MAT-file database using dpsssave.

example

dpssdir(seqLength) lists the sequences saved with length seqLength.

example

dpssdir(timeHalfBW,"NW") lists the sequences saved with time-half-bandwidth product timeHalfBW.

example

dpssdir(seqLength,timeHalfBW) lists the sequences saved with length seqLength and time-half-bandwidth product timeHalfBW.

example

index = dpssdir(___) returns a structure array index describing the DPSS database. To generate a filtered index, pass the seqLength and timeHalfBW options as in the previous syntaxes.

example

Examples

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Open Live Script

Create and manage DPSS sequences.

Generate four Slepian sequences. Each sequence has 128, 64, 256, and 64 samples, respectively. The corresponding time-half-bandwidth products are 1, 2, 3, and 4.

sL = [128 64 256 64]; % Segment length
tHBW = 1:length(sL); % Time-half-bandwidth product
for k=1:length(sL)
    [dpsSeq,lambda] = dpss(sL(k),tHBW(k));
    dpsssave(tHBW(k),dpsSeq,lambda);
end

List all the databases of Slepian sequences from the dpss.mat file.

dpssdir
File: C:\Example\dpss.mat
    N     NW    Variable names
   ---   ----  ----------------
     64  2.00  E2, V2
         4.00  E4, V4
    128  1.00  E1, V1
    256  3.00  E3, V3

List the databases with 64 Slepian sequences from the dpss.mat file.

dpssdir(64)
File: C:\Example\dpss.mat
    N     NW    Variable names
   ---   ----  ----------------
     64  2.00  E2, V2
         4.00  E4, V4

List the databases with a time-half-bandwidth product of 2.

dpssdir(2,"nw")
File: C:\Example\dpss.mat
    N     NW    Variable names
   ---   ----  ----------------
     64  2.00  E2, V2

List the databases with 256 Slepian sequences and time-half-bandwidth product of 3.

dpssdir(256,3)
File: C:\Example\dpss.mat
    N     NW    Variable names
   ---   ----  ----------------
    256  3.00  E3, V3

Display the index structure for all the databases of Slepian sequences from the dpss.mat file.

index = dpssdir
index=1×3 struct array with fields:
    N
    wlist

Input Arguments

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Sequence length, specified as a positive integer.

Data Types: single | double

Time-half-bandwidth product, specified as a positive scalar. This argument must be less than seqLength/2.

Data Types: single | double

Output Arguments

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Index of DPSS databases, returned as a struct array.

  • If you specify to return index and do not specify any input arguments, the dpssdir function returns the index variable in the dpss.mat file.

  • If you specify to return index and specify input arguments, the dpssdir function returns a filtered subset of the index variable in the dpss.mat file based on the values of seqLength and timeHalfBW.

  • If you do not specify to return index, dpssdir reads the index variable in the dpss.mat file and returns a table with these columns:

    • N — Sequence lengths.

    • NW — Time-half-bandwidth products.

    • Variable names — Variable names that represent the Slepian sequences (E1, E2, …, En) and their corresponding frequency-domain energy concentration ratios (V1, V2, …, Vn) for a DPSS database with n Slepian sequences.

See Structure of DPSS MAT- file Database for more information.

More About

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Structure of DPSS MAT- file Database

The dpsssave function creates and stores a file named dpss.mat with the DPSS (Slepian sequences) that you generate with the dpss function.

The dpsssave function assigns a location key (1, 2, …, n) and a name (E1, V1, E2, V2, ..., En, Vn) for each Slepian sequence that it generates and stores it in the dpss.mat file, from the first to the nth sequence.

A dpss.mat file with n sequences presents the following structure:

  • E1, E2, …, En — Slepian sequences.

  • V1, V2, …, Vn — Frequency-domain energy concentration ratios.

  • index — Database index, a struct array with information of the list of sequence lengths, time-half bandwidth products and locations of the Slepian sequences stored in the DPSS MAT-file database. This structure array comprises of the following fields:

    • N — Vector of sequence lengths. The dpsssave function assigns a single entry in N for each different value of sequence length.

    • Wlist — Structure array of time-half bandwidth products NW and sequence location numbers key. The dpsssave function assigns a sequence location key to each Slepian sequence each time you call it.

  • next_key — Next-sequence identification key, defined as next_key=n+1 where n is the number of Slepian sequences stored in the DPSS MAT-file database.

Version History

Introduced before R2006a

See Also

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