Algorithm 1 Two-dimensional sample entropy

Require: Sequence $\mathbf{U}:=\{u_{i,j}:1\le i\le w,1\le j\le h\}$, $\mathbf{s}\subset {\mathbb{Z}}_{w,h}$ template length m and   threshold r. 1:procedure SampEn2D($\mathbf{U},\mathbf{s},m,r$) 2:    Set $count=0$, 3:    Set $N_0=\#\mathbf{s}$, 4:    for $i=1$ to $N_0$ do 5:        for $j=i$ to $N_0$ do 6:           $(k,l)={\mathbf{s}}_i$; $(a,b)={\mathbf{s}}_j$, 7:           ${\mathbf{X}}_{i,j}^{\mathbf{m}}=\mathbf{U}[i:i+m-1][j:j+m-1]$, 8:           ${\mathbf{X}}_{a,b}^{\mathbf{m}}=\mathbf{U}[a:a+m-1][b:b+m-1]$, 9:           if $d({\mathbf{X}}_{i,j}^{\mathbf{m}},{\mathbf{X}}_{a,b}^{\mathbf{m}})\le r$ then 10:               $count=count+1$, 11:    return $count$