function yout=chis(x,varargin)
sigma=1;tail=0;alpha=0.05;yout=0;
if nargin>1
    tmp=varargin(1);
    if isnumeric(tmp)&&(tmp>0)
        sigma=tmp;
    end
end
if nargin>2
    tmp=varargin(2);
    if isnumeric(tmp)&&(tmp>0)&&(tmp<1)
        alpha=tmp;
    end
end
if nargin>3
    tmp=varargin(3);
    if isnumeric(tmp)
        tail=tmp;
    end
end
x=x(:);
n=length(x);
TT=(n-1)*var(x)/sigma;
switch tail
    case -1
        sui=chi2inv(alpha,n-1)
        yout=(TT<=sui);
    case 1
        sui=chi2inv(1-alhpa,n-1)
        yout=(TT>=sui);
    otherwise
        si=chi2inv(alpha/2,n-1);
        lian=chi2inv(1-alpha/2,n-1);
        yout=(TT<si)|(TT>lian);
end