YALL1-Group: A solver for group/joint sparse reconstruction

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YALL1-Group is a MATLAB software package for group/joint sparse reconstruction, written by Wei Deng, Wotao Yin and Yin Zhang at Rice University. Download

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Contents 1 Model 2 Syntax 3 Input Arguments 4 Output Arguments 5 Examples 6 Technical Report

Model

(1) Group-sparse basis pursuit model:

                  Minimize     
  
                  subject to   

where , , denotes the index set of the -th group, and is the weight for the -th group.

(2) Joint-sparse basis pursuit model:

                  Minimize     
                  subject to   

where , , denotes the -th row of matrix , and is the weight for the -th row.

Syntax

[x,Out] = YALL1_group(A,b,groups,'param1',value1,'param2',value2,...);

Input Arguments

• A: an m-by-n matrix with m < n, or a structure with the following fields:

1) A.times (required): a function handle for ;

2) A.trans (required): a function handle for ;

3) A.invIpAAt: a function handle for ;

4) A.invAAt: a function handle for .

Note: Field A.invIpAAt is only required when (a) primal solver is to be used, and b) A is non-orthonormal, and (c) exact linear system solving is to be performed. Field A.invAAt is only required when (a) dual solver is to be used, and b) A is non-orthonormal, and (c) exact linear system solving is to be performed.

• b: an m-vector for the group-sparse model or an m-by-l matrix for the joint-sparse model.

• groups: an n-vector containing the group number of the corresponding component of for the group-sparse model, or [] for the joint-sparse model.

• Optional input arguments:

Parameter Name	Value	Description
'StopTolerance'	positive scalar	Stopping tolerance value.
'GrpWeights'	nonnegetive n-vector	Weights for the groups/rows.
'nonorthA'	true or false	Specify if matrix A has non-orthonormal rows (true) or orthonormal rows (false).
'ExactLinSolve'	true or false	Specify if linear systems are to be solve exactly (true) or approximately by taking a gradient descent step (false).
'QuadPenaltyPar'	nonnegative 2-vector for primal solver or nonnegative scalar for dual solver	Penalty parameters.
'StepLength'	nonnegative 2-vector for primal solver or nonnegative scalar for dual solver	Step lengths for updating the multipliers.
'maxIter'	positive integer	Maximum number of iterations allowed.
'xInitial'	an n-vector for group-sparse model or an n-by-l matrix for joint-sparse model	An initial estimate of the solution.
'Solver'	1 or 2	Specify which solver to use: 1 for primal solver; 2 for dual solver.
'Continuation'	true or false	Specify if continuation on the penalty parameters is to be used (true) or not (false). The continuation scheme is as follows: multiply the penalty parameters by a factor if , where 0< <1 is a parameter, and denote the constraint violations at the current and previous iterations, respectively. Continuation allows small initial penalty parameters for constraint violations, which lead to faster initial convergence, and it increases those parameters whenever the violation reduction slows down. It leads to overall speedups in most cases.
'ContParameter'	scalar between 0 and 1	The parameter (0 < <1) in the continuation scheme.
'ContFactor'	scalar greater than 1	The factor in the continuation scheme.

• Note: the parameter names are not case-sensitive.

Output Arguments

• x: last iterate (hopefully an approximate solution).
• Out: a structure with fields:
  • Out.status—exit information;
  • Out.iter—number of iterations taken;
  • Out.cputime—solver CPU time.

Examples

Please see the demo files.

Technical Report

The description and theory of the YALL1-Group algorithm can be found in

• Wei Deng, Wotao Yin, and Yin Zhang, Group Sparse Optimization by Alternating Direction Method. (TR11-06, Department of Computational and Applied Mathematics, Rice University, 2011)