function?[s_hatsigma2_hatA_indexCount]=ExCoVapp（Hyvarargin）
%Approx.?ExCoV?routine:?
%Coded?by?Kun?Qiu?（kqiu@iastate.edu）
%updated?Feb?14?2009

%Function?usage
%=======================================================
%INPUT（compulsory）:
%H:??????????????????????the?sensing?matrix
%y:???????????????????????the?measurement?column?vector
%
%INPUT（optional）:
%‘Noi_Cov‘:????????the?N?by?N?noise?covariance?structure?matrix
%?????????????????????????（default=eye（N））
%‘FIR_len‘:?????????the?size?of?moving?average?window
%?????????????????????????（default=10）
%‘Init_mode‘:??????type?of?initial?sparsity?support?（valued?in?{01}）
%?????????????????????????0:?initialize?with?empty?set?
%?????????????????????????1:?initialize?with?a?crude?high?level?signal?components?support?estimate
%?????????????????????????（default=1）
%‘Visibility‘:?????????Option?to?see?visually?the?reconstrution?process?（valued?in?{01}）
%?????????????????????????0:?work?silently
%?????????????????????????1:?work?openly
%?????????????????????????（default=1）
%========================================================
%OUTPUT:
%s_hat:??????????????the?signal?esitmate
%sigma2_hat:????the?noise?variance?estimate
%A_index:?????????the?estimated?set?of?high?level?signal?components
%Count:?????????????Count?of?number?of?iterations
%========================================================

if?（nargin-length（varargin））~=2
????error（‘Missing?required?inputs!‘）;
end

[Nm]=size（H）;

%Setting?default?values?for?the?optional?inputs
C=eye（N）;
FIR_len=10;
Init_mode=1;
Visibility=1;

%Read?the?optional?inputs
if?（rem（length（varargin）2）==1）
????error（‘Optional?inputs?must?go?by?pairs!‘）;
else
????for?i=1:2:（length（varargin）-1）
????????switch?upper（varargin{i}）
????????????case?upper（‘Noi_Cov‘）
????????????????C=varargin{i+1};
????????????case?upper（‘FIR_len‘）
????????????????FIR_len=varargin{i+1};
????????????case?upper（‘Init_mode‘）
????????????????Init_mode=varargin{i+1};
????????????case?upper（‘Visibility‘）
????????????????Visibility=varargin{i+1};?????
????????????otherwise
????????????????error（[‘Unrecognized?optional?input:?‘‘‘?varargin{i}?‘‘‘‘]）;
????????end
????end
end

Inv_HH=inv（H*H‘）;
C_inv=inv（C）;

scale=sqrt（N/（y‘*C_inv*y））;
y=scale*y;

%Initialization
if?Init_mode
????ma=floor（0.5*N/log（m/N））;
else
????ma=1;
end
mb=m-ma;
u=H‘*Inv_HH*y;
u_sort=sort（abs（u）‘descend‘）;
A_index=find（abs（u）>=u_sort（ma））‘;
B_index=1:m;
B_index（A_index）=[];
HA=H（:A_index）;
HB=H（:B_index）;
s_A_init=u（A_index）;
sigma2=（y-HA*s_A_init）‘*C_inv*（y-HA*s_A_init）/N;
delta2_a=10*sigma2*ones（ma1）./diag（HA‘*HA）;

expand=1;
compress=0;
exit_flag=0;
Count=0;
p=0;
A_index_record_pre=[];
GML_star=-inf;
GML_record=-inf;

if?Visibility
????figure（1）
????set（gcf‘color‘‘w‘）;
????subplot（211）;
????plot（-inf-inf）;
????axis（[0N0500]）;
????xlabel（‘Sparsity‘‘Fontsize‘12）;
????ylabel（‘GL‘‘Fontsize‘12）;
????title（‘Now?