function?[xstatushistory]?=?l1_ls（Avarargin）
%
%?l1-Regularized?Least?Squares?Problem?Solver
%
%???l1_ls?solves?problems?of?the?following?form:
%
%???????minimize?||A*x-y||^2?+?lambda*sum|x_i|
%
%???where?A?and?y?are?problem?data?and?x?is?variable?（described?below）.
%
%?CALLING?SEQUENCES
%???[xstatushistory]?=?l1_ls（Aylambda?[tar_gap[quiet]]）
%???[xstatushistory]?=?l1_ls（AAtmnylambda?[tar_gap[quiet]]））
%
%???if?A?is?a?matrix?either?sequence?can?be?used.
%???if?A?is?an?object?（with?overloaded?operators）?At?m?n?must?be
%???provided.
%
%?INPUT
%???A???????:?mxn?matrix;?input?data.?columns?correspond?to?features.
%
%???At??????:?nxm?matrix;?transpose?of?A.
%???m???????:?number?of?examples?（rows）?of?A
%???n???????:?number?of?features?（column）s?of?A
%
%???y???????:?m?vector;?outcome.
%???lambda??:?positive?scalar;?regularization?parameter
%
%???tar_gap?:?relative?target?duality?gap?（default:?1e-3）
%???quiet???:?boolean;?suppress?printing?message?when?true?（default:?false）
%
%???（advanced?arguments）
%???????eta?????:?scalar;?parameter?for?PCG?termination?（default:?1e-3）
%???????pcgmaxi?:?scalar;?number?of?maximum?PCG?iterations?（default:?5000）
%
%?OUTPUT
%???x???????:?n?vector;?classifier
%???status??:?string;?‘Solved‘?or?‘Failed‘
%
%???history?:?matrix?of?history?data.?columns?represent?（truncated）?Newton
%?????????????iterations;?rows?represent?the?following:
%????????????-?1st?row）?gap
%????????????-?2nd?row）?primal?objective
%????????????-?3rd?row）?dual?objective
%????????????-?4th?row）?step?size
%????????????-?5th?row）?pcg?iterations
%????????????-?6th?row）?pcg?status?flag
%????????????-?7th?row）?CPU?time?（added?by?Mario?Figueiredo?on?16/06/2007）
%
%?USAGE?EXAMPLES
%???[xstatus]?=?l1_ls（Aylambda）;
%???[xstatus]?=?l1_ls（AAtmnylambda0.001）;
%
?
%?AUTHOR????Kwangmoo?Koh?
%?UPDATE????Mar?4?2007
%
%?COPYRIGHT?2007?Kwangmoo?Koh?Seung-Jean?Kim?and?Stephen?Boyd

%------------------------------------------------------------
%???????INITIALIZE
%------------------------------------------------------------

%?IPM?PARAMETERS
MU??????????????=?2;????????%?updating?parameter?of?t
MAX_NT_ITER?????=?400;??????%?maximum?IPM?（Newton）?iteration

%?LINE?SEARCH?PARAMETERS
ALPHA???????????=?0.01;?????%?minimum?fraction?of?decrease?in?the?objective
BETA????????????=?0.5;??????%?stepsize?decrease?factor
MAX_LS_ITER?????=?100;??????%?maximum?backtracking?line?search?iteration

%?VARIABLE?ARGUMENT?HANDLING
%?if?the?second?argument?is?a?matrix?or?an?operator?the?calling?sequence?is
%???l1_ls（AAtylambdamn?[tar_gap[quiet]]））
%?if?the?second?argument?is?a?vector?the?calling?sequence?is
%???l1_ls（Aylambda?[tar_gap[quiet]]）
if?（?（isobject（varargin{1}）?||?~isvector（varargin{1}））?&&?nargin?>=?6）
????At?=?varargin{1};
????m??=?varargin{2};
????n??=?varargin{3};
????y??=?varargin{4};
????lambda?=?varargin{5};
????varargin?=?varargin（6:end）;
????
elseif?（nargin?>=?3）
????At?=?A‘;
????[mn]?=?size（A）;
????y??=?vara